That and the fact that they will inevitably lose their data when they mishandle or misplace their keys. In the rare case that they are the sophisticated type o

That and the fact that they will inevitably lose their data when they mishandle or misplace their keys. In the rare case that they are the sophisticated type of user who will most likely (and even that likelihood could be debated) safely handle and retain their irrecoverable secrets, they're already solving their problem by doing client-side encryption on their own. Maybe that's what you meant by convenience/user experience. Client side encryption with a nontrivial, irrecoverable key that must be remembered and kept secret by the end user is not a very usable system for the vast majority of people.