Why? The more people adopt it, the more opportunities are available that it can be used daily. With bitcoin both ways can be used together. Just because someone else uses a custodian, doesn't mean you have to, but if no such custodian exists, they won't bother with bitcoin at all and then the opportunity to exchange bitcoin instead of fiat is gone. The "purist" mentality that ALL must use bitcoin in the most self-sovereign form is what will hold it back. I think that is the way it should be used, but I realize only a tiny minority of people will ever do it. It is like the Richard Stallman stance, not that he is wrong about free software... but the majority will never adopt his purism stance. But I guess we can all just HODL our bitcoin and zap each other.