The incentives to self custody already exist (rug pulls, censorship, etc) ecash isn't to scale self custody, it's to make already existing custodians better. I don't think custodians are ever going away, we just want them the be the best and most private experience.
Discussion
We don't need them to go away, we just need to offer similarly useful self-custody solutions... somehow...
As much as i agree that this would be the ideal outcome nobody seems to have anything remotely close to this. In the mean time we can still embrace the benefits this gives over the existing options.
Ecash is still a step forwards in a lot of ways compared to custodial lightning wallets.