There are no alternatives to exchanges right now so people have no choice but to take the risk of using an exchange platform for their trading activities. Until a real DEX platform arrives people will stick to this centralized custodial exchange for their money.
Gemini has a banking charter, is run by identifiable people, has a Bitlicence and abides by all known laws.
Bitfinex... does whatever it wants, doesn't tell anyone fuck all and ignores all regulation until it becomes too hot for them.
There are degrees of respectability.