For now funds at Swan are protected by same big trusts that manage coinbase and others. This firm ( forgot name) has 50/60 % share of CEX funds. So they encourage self custody but actually not practicing it. This is not pointed out enough.
Prime Trust. Apex is another big player. Both handle the backend clearing for lots of exchanges. I think the regulatory burden is a major reason companies use these brokers, it can save a lot of time going to market.