I've reached this conclusion at least or at most I don't know but thanks to the comments,...please do reply ,I'm still processing & open to every thoughts.
Your sexual appetite is like your appetite for food. Some people can eat steak and potatos their whole life and not get bored; some people want variety. Whether you like corn, cauliflower or whatever vegetable probably depends on how and what you were served as a child.
I think that we are hardwired for occasional 'other' sexual activity because it kept the species alive by working on something in our psyche, just like eating a variety of food gaves us all the nutrients we need for our body.