That's not quite correct.
The problem with subprimes was that banks were issuing questionable loans, and then selling them to investors (Without telling them that the loans weren't worth the paper they were printed on.)
This carries a significant reputation risk because they were, quite literally, defrauding their customers.
A crypto trading desk, on the other hand, just lets them buy or sell crypto on a customer's behalf, and charge them a fee for it - much like Coinbase does for retail customers. They won't have any insider knowledge about crypto, and they probably won't even care if BTC goes to $100,000 tomorrow, or to $0. The customer asks the bank to sell them BTC, the bank gives them a quote, and the customer accepts or rejects it. The bank doesn't know if its a good price, nor does it care - and the customer knows that the bank doesn't know, or care.
There's still ways to defraud customers in this arrangement, but there are far fewer incentives to do so... Compared to offloading toxic, shitty mortgages off your books, after having bribed ratings agencies to rate them AAA.
If you really care about crypto, this is a Good Thing (tm). Currently, the counterparty risk with Bitcoin exchanges is through the roof. Some of them allow illegal wash trades, some of them don't follow KYC, some of them go belly-up and steal all your bitcoin and dollars, some of them may be front-running their users, some of them don't allow half their users to withdraw USD, some of them are down for minutes a day... For anyone trading in an extremely volatile environment (Like Bitcoin), this practically screams: "RUN, DON'T WALK AWAY."
The counterparty risk with a Goldman Sachs trading desk is... Much lower.