Because the candidates do have those responsibilities, but have shirked them. Ideally, we’d want a better voting system, that didn’t mathematically garuntee that only two viable parties emerge, so that when the politicians refuse to use their power as they should, people who will may be chosen instead, but we don’t have that, and changing that is a long and difficult process that only gets harder if the more authoritarian types get power anyway. If you’re in a lifeboat with holes, and there are two people that have rigged things so that one of them is going to be in charge, and one wants to stop bailing out water and the other wants to scoop it back into the boat, then even though those two aren’t following their responsibilities, it doesn’t mean you should stop bailing the water out, because it has to get done by somebody or you drown. And if you have a say in which of the two is in charge, the guy that just wants to sit there uselessly is still the option you must pick, because at least they aren’t trying to undo the progress you’re making. Ideally you’d want to figure out how to undo the rigged system too, but you have to deal with the water first, lest you all drown fighting over who’s in charge.