Yep, it's at least partly this. I watched a lot of "moderate" academics become "liberal" after Trump's first election.

If you're a scientist by principles and a moderate by political views, and the right-wing party comes out in opposition to science, well, it's fair that you might then join the "pro-science party". Being pro-science becomes a liberal position.

So it's not that conservatives were "purged" from the ranks of academia.