Users, when you ask them, want a service that handles the backup and synchronization of their identity between all their devices. Users don't want losing the device their keys are on to mean losing their identity. Users want to be able to join a new device to their identity by just entering their username and password on it. Users want to be able to enter those credentials on random public computers to be able to temporarily use their identity on those computers, then log out when done. And users don't care about the security implication of any of this.

Currently, given this set of use-cases, "identity providers" like Facebook and Google work perfectly for users. Password managers don't.