It doesn't, because they have options.
Based on what we know about the proliferation of broker accounts and apps at places like Coinbase, Binance, PayPal, etc., not to mention the ETFs, it would appear that
most consumers don't want self-custody and would instead prefer to keep an account secured by their own identity at a firm they trust.
It's important to understand the phenomenon of
the Anon Paradox, which states that consumers like anonymity for "small" money, and their personal identity connected to "big" money.
In other words, if somebody wants to play around with say $50 in Bitcoin or some other digital currency, then they want this to be anonymous like the physical cash in their physical wallet. The reason is that they like the anonymity for spending it--that way they don't impart personal data when they buy something.
But if somebody is keeping a large part of their life savings digital currency investments, they want this to be safe and they tend to want to enlist the services of a firm like Coinbase to guard their money for them because they would otherwise be afraid of losing the keys, or them being stolen, or them being beaten or murdered because of their physical possession of their keys (it's the same reason people don't hold their savings in piles of physical cash in their own home and instead use a bank).