Because society teaches us to do so. Further, I work with a Developmentally Delayed individual and his way of showing unbridled glee when he is happy is... disconcerting.

While I agree with you that we should feel free to, feel and show same, I do think that being too unbridled can lead to problems. Partially because folks might be discomfitted (and to an extent I say 'fuck 'em' to that). Partially because... well, if you let it go too far and have NO filters (trust me, filter free is what we deal with at work) then you are likely to send signals unintended.

Imagine greetind someone you like (lower case) with a bunch of happy warm fuzzies, hugs and maybe a peck on the cheek as if you LIKE them. What message might they get from that? Heck, we guys have a history of misinterpreting a simple smile... imagine the next girl greating you with an all encompassing hug AND a smile... if we had perfect control, this would be ok, but us guys don't have a great track record (for the record, I have not been accused of going too far in reaction to a smile or other greeting but I have had women react poorly to greetings and have read a LOT of accounts of problems caused by... misinterpretations, so, I won't pretend it's not out there).

The short of it is that we learn, within our culture, how far our culture accepts us displaying emotions. That, unfortunately, can lead to suppressing same and THAT is a grade A tragedy. We need to be more accepting of the fact that we are emotional beings and we need to be able to let them out and play on occasion. So that we can talk about them, and get help with some of the less tame ones (depression, anger, etc).

Good question/comment, by the way!

I am quite a bit older than you and have learned this over the years: live your life with your arms wide open. That is a metaphor for not hiding your feelings, not pretending and not playing a role to get an advantage. As a consequence of this, I am not powerful, not rich, not feared. I am beloved and admired and sleep well at night.

From my POV have seen people who are repressed because they were forced to "squish" their feelings. Their feelings were invalidated or they were punished for them somehow.
It can start in early childhood. "Don't cry" after a kid bumping their head or getting scared , etc, instead of letting a kid have their feelings and talking them through with them some who aren't equipped or willing to bother would rather just shut the kid up and it carries into adulthood.

For me it began in childhood due to my mother's second husband getting off other people's misery. The more impassive I was, the more I "won". It was why I so idolized the charactor Spock on TOS.

My younger brother died when I was 30 and I was not speaking to him at the time.I had been estranged from my father most of my life and had just recently reconnected with him so after my brother's death my father and I did some talking and when he died a few months later, I was much less distraught than I would have been otherwise.I became more open about how I felt but then fell into a relationship where it was used against me.

I still struggle because people attach more meaning or depth to the things I say.. For example, I man I was socializing with mistook me saying "... I know enough about you to know I like you" as a a statement of romantic interest. He was quick to let me know he had no romantic interest and didnt want to hurt me etc which was kinda embarrassing and made me go back and try to remember every conversation I had had with every male and dissect them for suspected hidding meanings.

So it is easier to just be an over the top smartass

Verbal communication is sometimes overrated. I do find that the cliche. Actions speak louder than words to be more than a mere axiom. Also some people are visual and/or kinetic learners, so find coommunication via these elements easier and possibly more meaningful. . . . But everyones different. - and the english are (in)famous for their reserve.

Because people fear being judged,institutionalized and ridiculed. So people will hold in their emotions as a defense mechanism. Best thing for people do is find a network of friends and family that can all come together and help one another with no strings attached.

You would have to ask all people to know why they hide there feelings. you let them out with facial expressions, body language and vocally.

Fear.

I didn't hide them. I misplaced them, and just like my keys I'm not sure where to look.

If you are dealing with a controlling and manipulative person, the more you eveal your emotions, the the more tools you give that person to play "mind'fuck" games with you.

A person who is emotional is not rational. If a person is not rational, nothing they say or do has any validity. A person who must exprees their emotions is a weak person...anoying to be around.

I hide my emotions only in so much as not wanting to piss you off and make you want to fight. No need for that. I can get my point across and if I do not agree with you I tell you so. I do not shoot guns for recreation to keep my anger inside or control it. I do not hold grudges (real or imagined) against anyone. (Well, wait. Maybe at Trump.) I do not wake up in the night hating Charlie or Susie.
I let my emotions out by just doing normal things that I like. No need to pull legs off insects or kill animals. Nothing hiding inside that wants to shoot adults or school children. I'm not worried that you are "against me" or "planning something" that might involve me. Maybe that's because I do not live in that kind of world.

I have D.I.D I'm pretty immediate with my feelings, but have never grieved for people who died, I wondered if it was coming from an abusive family that made me not care about death -

I'm very emotional.

Insecurity. they feel insecure so they tend not to let others in for fear they will be harmed.

Interesting. Not everyone wants to talk about their problems all the time. Also something that makes you sad is one aspect of your life and doesn't have to define you. Are you asking about clinical depression? That would be a different ball game. As for telling people you like them, sure, but how you respond afterwards is the trick, if it's not mutual it can be a bit awkward can't it? But a good friendship can ride almost anything out, sure!
Still feel I'm not answering this as well as I could, but will leave it there. I'm a generally honest and open person, but there are exceptions to most rules!

Why?...fear, which can lead to guilt, shame and much more. Bipedal humanoids are bread to be a collective group, not living alone, we need each other. So people want to have people around them, they want to make those people happy and so maybe they hide their sadness to make sure others around them don't get sad. I can think of many reasons people might hide their true feelings, this is just one.

Let out a good cry everyonce in awhile . Pretending honestly always made me sadder.

I’m very introverted and even misanthropic and just don’t wanna connect with people in general. Emotions can make you vulnerable, and fuck that. I’ve found that if I keep my emotions hidden I can then critically analyze them and thus get over them.

In my case is cultural; to most Argentinians to show emotions is a sign of low upbringing

I was taught, at a very early age, to keep my feelings and emotions to myself. It is a lifelong habit.

One can not control ones emotions. One can only choose to act upon them or not. It is the mature who do this. It is the undeveloped mind that has no self controlling mechanisms. No impulse control. I am vastly more mature than I once was. Challenging myself to grow by choosing what emotions I wish to act upon or not.

When I was younger, during my first real experience of love - I didnt reveal my feelings to my partner - I thought my feelings were obvious -
my computer keeps crashing and I have to start again - frustrating
But she left me as she thought I didnt care - I didnt understand at the time - I thought my feelings were so obvious, but apparently not - so Id advise people not to keep their feelings to themselves to make their feelings known to others - as it can cost you if you don't share your feelings - I still regret my actions even though they were a long long time ago!

Okay.

I hid my emotions because I was made fun of for having them by everyone. I laughed and cried "too much". So, that stopped.