Why? He won't "officially" control it, but has a lot of influence (see all the other briberies, I mean donations, he did). SBF is one sneaky bastard that knows very well what he's doing.
Yes, they're criminals who belong in jail but only for the way they managed their balance sheet. They were also great builders who had awesome products and wanted to do all the great things they said they wanted to do.
Buying a bank is something probably every crypto exchange has considered doing, so they can have access to the financial system and not have to pay massive amounts of money and have huge headaches processing payments for their customers. I'm surprised Coinbase doesn't own one by now - or perhaps they do.
I think SBF was VERY informed, especially looking at his background. It's simple greed for power (not even the money).