That's because the things they can't get him on (yet) include inciting violence intending to prevent the lawful transition of power (aka a coup attempt) -- because the judge is deferring the case past the election -- and influencing states to cast votes in the electoral college against what their people voted for -- because the case is on hold pending investigation of the prosecutor. Both of those have already resulted in convictions of multiple Trump staffers; Trump himself has managed to delay justice in both of those more serious cases.

There is a reason they got Al Capone on tax evasion, and it wasn't because that was the worst thing he did. Crime bosses are notoriously slippery.