This Manhattan case may be one of those "it's not the crime, it's the cover up that'll get ya" kinda deals. While falsifying business records might be a misdemeanor on their own, they can be elevated to a felony if it's in service of concealing or committing other crimes. I can see this reasoning being used, especially since we have not 1 but possibly 30+ counts.
Please remember that the timing is partly because Trump was actually US President for FOUR of those years. There was no way they would have been able to move on this case (subpoenaing the officials & attorneys, the people pertinent to the case that they needed to question) nor bring it to completion while he was in the Oval Office. We already know that there's a reluctance to charge a sitting President due to that memo, it's an untested legal precedent. Can you imagine what the screams of "political witch hunt!!" would have been like DURING his presidency? So the timing is what it is, because it has to be this way to be the LEAST political. And Trump has known all along (in my opinion) that the only way to escape all of these impending criminal and civil investigations is to constantly be in the Oval Office. It's his get out/stay out of jail card for now.
It's the chickens coming home to roost imo. Accountability is extremely important, especially in one's high ranking politicians. There would never be a convenient time for criminal charges to come down for DJT. It would always be called politically motivated, "fake", "monstrous", "witch hunt" etc. Because that's the kind of incendiary rhetoric Trump uses regularly about anything even remotely negative about himself. JMO.