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.
I think the key phrase here is "in the long term". Who says Bitfinex is in it for the long term? They say it? Why do you trust them?
A typical business will try to make money off you any way they can, scamming you if they deem it is profitable. The more legally gray area the business is in, the more likely it is you'll get scammed.
I think 'oolongCat was trying to point out that a centralized Bitcoin business may very well understand decentralization perfectly; that doesn't mean they will care about it in any way.