It's really nice to have this kind of privacy, but I don't understand how people can use a service like this while they don't provide the ability to make local

It's really nice to have this kind of privacy, but I don't understand how people can use a service like this while they don't provide the ability to make local (encrypted) backups. If their servers disappear for whatever reason (legal issues or hardware problems), you end up with 0 e-mails. Nothing. Tutanota.de has the same problem, no backup feature.