Corruption.

They were both truly awful options. But the blatantly corrupt one lost. And I do like to see corruption lose.

Of course, Trump is probably corrupt too. He runs a casino-cum-strip-joint, for God's sake (though if he were properly corrupt, perhaps it wouldn't be going bankrupt). But he isn't blatantly corrupt: he recognises that corruption is supposed to be hidden, so makes some attempt to hide it. Clinton's attitude to the public has been one big "Yeah, I'm lying to you and taking massive bribes, and what the fuck are you going to do about it?" She didn't even attempt to make her lies believable:

"Did you wipe your server?"
"What, like, with a cloth?"

At least, when you try to fool people, you accept that they are worth fooling. When you make your lies so obvious that it's impossible to believe them, you ask your listeners to join you in the deceit. You're telling them up front that they're as bad as you are and you know it.

I'm cynical enough to accept that there's bound to be some corruption and indecency at that level of politics. But I also believe that the public's refusal to accept that corruption when it's discovered is a necessary check on its extent. That was the thing about Clinton: not just the corruption, but the blatancy. I'm sure Trump has taken and given a lot of back-handers in his time. Clinton turned them into front-handers.