Why do people just believe what they are told without questioning it???
People believe what they are told if it agrees with what they already believe. If it doesn't agree with what they believe, they ignore it.
The simplest explanation is always overlooked. We are and have always been herd animals. Think not? Stand in the front of an elevator where you know no one and try to turn around and look at the people. No matter how hard you try not to laugh or jump in a movie theater -- and while you may not give any outward sign -- you still react with the rest of the people in the theater. When one breaks with the herd, one becomes asocial (look it up). We still have a long way to go before we can overcome our baser needs.
Simples: one of the things they are told, and believe, is that they durst not ever question it.
The Bible goes on at length about this. It is anti-intellectual, anti-reason, and pro belief in unsubstantiated assertions of dogma. It styles the latter as virtuous and any form of critical thinking as blasphemous.
It's easier I suppose, as it requires taking no time whatsoever to think for themselves.