When they experienced it with their own capital, lost their capital, they will no longer see that using a self-custodial (non-custodial) wallet is too difficult in practice.
You will not believe that despite some people losing their funds to an exchange or any custodial service, these same people will still store some of their coins in other centralized exchanges, in the believe that they are safer that the one that collapsed. It sounds hard to be true, but it happens, some people simply believe that self custody is not for them.
One can still lose funds when stored in their self custody, but that is if they do not know what they are doing or if they do not have enough knowledge on how to secure their funds, if they do, they wouldn't lose it.