Or some people, like me, want to make others happy. If letting them have their way makes them happy why not? The exception to this is children. Give them their way all the time and you're creating a selfish brat. I'm talking about adults. If I don't have a strong opinion about a particular thing, I will give other person what they want. i.e. like where to eat out.
Peer pressure is responsible for most mindless compliance. Some people are simply too lazy to think for themselves, so they just go with the flow. Also, they may lack the self confidence necessary to go against the majority.