The problem is that they bet with an illegal bookie and owed him massive amounts of money. That can obviously cause a bad situation where they leverage Otani and start making him do stuff like strike out on purpose a few times to manipulate some prop bet.
With any of the legal betting places you have to put the money up before you can place any bet, so this situation couldn’t happen. And players are allowed to hide these as long as they aren’t betting on baseball.
My prediction here is that they never find evidence that Otani himself bet on any baseball games but they’ll have to punish him for having direct dealings with a bookie. I’m going to say they give him 40-80 games to send a message but not totally ruin their new golden child. The dodgers are good enough to stay in contention without him for half the year and Otani would still have 8.5 or 9.5 years left to put this behind him. Ippei, I assume, will fall on the sword shortly and literally.