Why are there so few economists and libertarians in elected office?
Economics: I think that if somebody thinks they can decide things for other people, they do not understand economics. If you understand economics, then you are humble and modest. Of course, that would explain why there are so few economists in elected office. You have to have a large amount of confidence that you can help people by forcing them to do things they wouldn't otherwise do.
Libertarianism has a philosophical problem in that the better a libertarian you are, the less likely it is that you will seek to control other people. The Libertarian Party is at best an effort to do the least bad possible, and who would vote for that? You're more likely to be successful in preventing the most bad by voting for the least bad major party candidate.