One probable reason is that it helps promote peacock, NBC's streaming service that airs some of those shows. The Office's official Twitter even changed it's name to include peacock in the name

I could be totally wrong but I've seen speculation from others online and in videos saying it matches some old animated holiday specials. But I have no real evidence anyway so who knows, haha?

I believe the animation style was a direct choice to mimic 80's animated holiday specials. There were a lot of little style choices made to match old holiday classics. Also totally possible you're right and Rooker was busy but I am leaning towards style choice. I'm sure Gunn will be open to answer it at some point when asked.

Makes sense. There were several times where I could tell that they were editing around him as he didn't necessarily share the same shots as the other cast members. They'd be at the dinner table and he'd be at the end. Or they'd be in a room and he'd be sitting on the couch/recliner so they could cut to him. But it wasn't the same as the first few seasons.

Yeah he was apparently making people uncomfortable and was asked to stop/behave himself and he basically blew off the warnings and acted like he wasn't causing any problems. Apparently he was probably just not fun to work with. It was clear in recent years they were kind of shooting around him or not using him with everyone as much