The DNC has been later in August in the past, according to this page on wikipedia. Same goes for the RNC.
But I don't know if Ohio's law has always been this way or if it's newer. Either way, it sounds like in the past that various states have had provisions for this scenario, knowing that this could and did happen. So if I had to guess, the issue is that, like many things in our political system, we relied on traditions and cooperation to maintain the system. And of course, Republicans for the last 8yrs (longer than that, really) no longer want to do that. They'd rather see it all burn down in the name of DJT.
Oh god, please no. I need some mind's-eyebleach.