That's it, really. I don't think there is any other reason. The one thing that unites most Republicans, well, it isn't tax policy. And it isn't racial resentment. It isn't even hating "the gays".

It's that they like to see Democrats lose. It's a trip for them. The idea that Democrats might celebrate, might be on top for once, is too much for many of them to tolerate.

See this link for more.

Oh, and this tweetstorm, https://twitter.com/JoyAnnReid/status/877362133855371264 makes a related point.