If you’re looking for an actual answer: they don’t want to give up the power they have. They think they know better, when in the vast majority of situations, they have no fucking clue what they’re doing. Just like the rest of us.

Direct democracy for everything isn't a solution either. There're many complex problems where a short summary isn't enough to make an educated decision (just like voting).

Additionally, people often enough only read the headline and come to their conclusion. This would open up the door to even more populism, where the deliberately misinformed majority decides for all.

Not that I'm against more direct democracy, especially for laws where all people are directly and heavily affected (e.g. abortion).

Disclaimer: I'm not an US citizen, so voting is probably more fustrating for you with only two parties. It's already difficult enough to vote for a party with more options.