It would be completely on-brand for the dems to slow roll the prosecutions only to have the entire thing blow up in their faces and let a criminal off the hook.
That said, the Jan 6 prosecutions followed the traditional, deliberate bottom-up approach. The classified documents case was derailed by a maverick Trump judge but would eventually see a jury. The Georgia state charges were hamstrung by their chosen RICO path and Willis's ill-advised romantic entanglement. It could be that Biden and the DNC stayed out of it in a deliberate attempt to take the high road and/or avoid handing Trump a political defense.
On January 7 everyone thought Trump's political career was over and that he could only delay justice. Alas, he set up a very large inflation time bomb in 2020 and the rest is history.
If my suspicion is right, that was one of the more spectacular political miscalculations in American history. If I'm wrong... well, maybe the DOJ was investigating and stuff, but from the outside it looks like they wasted a year that they really could have used.