Assuming they don't plan to die tomorrow, Bitfinex is on the hook for a lot of money to a lot of people right now, and they're likely going to be sued. If they were only in it for the short term, they weren't in it for short enough; they didn't get out in time. Where does Bitfinex benefit from this? If their intent was to scam their users, they've also scammed themselves through their own lack of understanding.
I get what you're saying, but it just doesn't work out, even as a short term scam, for reasons that are obvious to anyone who understands decentralization. Bitcoin centralization can be a way to execute a scam (see various darknet markets that have exited with all their users' escrow Bitcoins). But Bitfinex didn't use centralization to execute a scam. They just failed because they didn't understand how decentralization would affect their business.