Yes, I think powerlessness is a big part of it. I have a grandfather who is very concerned about America's problems and talks about things often. But he always says "what are you going to do about it?", rhetorically, believing that there is nothing you can do about it.
Another thing is that most people are totally ignorant about it. Imagine if you knew nothing about, say, rugby, and a huge rugby fan talks on-and-on about it trying to convince you what team is better than another and why, and why you should care. You might want to get away or change the subject. Mathematics, religion, medicine - or anything else you may not already find interesting, even if it is relevant to your life.
It takes great strategy and skill to teach people. I think a great method is the use of analogies and comedy. One must also be temperate and calm. As soon as you get all excited about it and go on a rant, you lose people and look crazy.
"Talk all you can about all you know all of the time."