The problem is that Attorney General Garland, for reasons known only to himself, wanted to wait until after the Jan 6th committee issued its report before turning the full power of the DOJ on prosecuting Trump.
I think he did it for political cover; to avoid the appearance of a political motive; but I think it’s obvious now that it was a mistake both because Trump was always going to claim political persecution regardless, and because they are now in real danger of running out of time.