Indictments don't come overnight. Yes, it's been a long time coming, but often prosecution doesn't happen until an airtight case has been established. We see this with work being done with lower-level investigations into Trump currently underway. I'm better that many of the former Trump staffers being called in are being offered the choice to flip on Trump or go to jail themselves.
Garland may be waiting to see what happens in New York and Georgia before pulling the trigger on federal prosecutions. Letting states take care of Trump may give an equally satisfactory outcome without the hoopla of federal prosecution, thereby leaving the precedent of not prosecuting a former president intact.
If the GOP takes congress, investigations is all they'll be able to do...Biden still controls the DOJ for another two years. Merrick Garland isn't going to start prosecuting anyone just because the Republicans think he should.
And by the way, if you haven't noticed, the democracy is already unstable.