For exchanges that aren't inside US jurisdiction like Binance, they will trade against their customers, use their customer deposits for whatever they want, and then when shit hits the fan, executives take the money and then go on a run or just quietly disappear. This has repeated countless times.
For exchanges like Coinbase, which is more regulated and a US public company, they are crooked because they know they're facilitating the trading of unregistered securities. It just so happens that our government is extremely slow at brining clarity to this sector. But for Coinbase, they're trying to milk this as much as they could - knowingly selling and marketing scams, ponzis, unregistered securities to their customers.