The critical virtue of self-custody and decentralization is not about if the user wants it or not, but just being always an option. If self-custody is always there yet used by none, it will never be the same as if it's not even an option, even if the end result superficially (yet deceptively) appears to be the same.

Lets say that in your city there's a bar "A" that's so good that everyone in the town goes to have their beer there exclusively. It's everyone's choice to do so. So the one who made that statement comes to this city and concludes "we don't need to be able to have more bars because truth is no one wants to go to other bar". The major of the city agrees and, since it's superficially the same, passes a bill so that now no one is allowed to go to any other bar but the "A" bar. Everyone is making that choice anyways, so there should be no problem at all... right? No one will agree, and that's why you need the possibility of having other bars to be an option, not necessarily to be used. It just has to be there, even if standing still forever.

And that's my postulate: self-custody and decentralization simply must be there, even if not used at all, ever. Their sole presence, the sole fact they can always be an option, is what disciplines everything from the bottom up, not their actual use.