There are still some republicans that think they can shed Trump and return to the good ol' days of neo-conservatism. They think Mitt Romney might actually matter again. That kind of thing.
They're wrong, of course. But they'll learn that in time.
Some others just don't see a future for themselves in a populist platform, even if it's called republican. I'm betting you see at least 5 to 10 republicans change teams and start calling themselves democrat just to stay in the game. Voting for impeachment is a surrender flag