I am going to guess most people here are from the UK. When Trump was president he did things that f'ed the whole world, and caught the attention of this forum more. With Biden, he is going to be doing things f'ing mostly Americans, so people care about it less.
A full 30% of the trump presidency thread was pivot jokes so it makes sense that this isn't as active.
Add some 50% comments and jokes about Trump's personality, tweets, and appearances, as well as comments on interpersonal relations within the administration and ensuing theories about upcoming implosions, fights, reveals, and you have a thread that was incredibly light on actual policy comments and discussion. Cut all that away, and you have a posting frequency that's probably not very different from this thread.
In 4 years all Trump got out of Congress was appointing judges and a tax cut that partly reverts in 10 years. He didn't get his border wall heavily funded, and was trying to divert funds from DOD to do it, and more importantly he didn't get rid of the ACA which was one of the main things he ran on (mainly because Obama's name is on it). McConnell put the partial repeal of the ACA to a vote and famously came up short with McCain not voting for it. So I don't know where this notion of "this never happens to Republicans" comes from.
Trump was extremely combative, pig-headed, vain, and simply destructive on just about anything though. It wouldn't have been the same if the GOP had had someone from within their own ranks in place, be it a clever political operator or another figurehead-type figure like Bush Jr. Surely Biden fits more in the latter categories; his relation to the Democratic party and caucus is nothing like Trump's to the GOP's.