It's probably a bunch of reasons. The first one that comes to mind is that the bad guys had a bunch of kinetic options all lined up, from BLantifa rioters to little green men to military distractions, and letting them appear to take office kept them wrong-footed. The next is that this is a great setup to mock the mockingbird media, which hamstrings the dangerous msm. Another is that it got a lot of arrestees in one place, which is logistically desirable. One more is that the appearance of Biden taking power allowed them to see the overseas players playing their cards: making conditioned payouts, issuing next-step instructions, and stuff like that. But I'd like to see more reasons and theories.