Have they? They keep voting for such politicians. People should think about the system of govt they want so that they can actually CHOOSE who they want, rather than this current farce of a system.
Sure, they could vote for a third party loser, but he/she would have no chance whatsoever to effect the major parties. Trump, OTOH, was exactly that, someone who didn't need party money and thus wasn't under the party's thumb. He also represented a major threat to democrat hegemony if he could actually win.
And it's working. The GOP leadership cannot ignore Trump and have to deal with him. The way the democrats dealt with Bernie was revealed and many are tired of that party's malfeasance as well. It remains to be seen, though, if the democrats will rally to hold their leadership to account or if they've become so accustomed to authoritarianism that they can't.
We need at least 3 or 4 major parties to force compromise and provide more choices for voters, but until the 2 we have now are forced to relinquish some control, we won't get them.