This is a result of LEAs not adjusting to the modern world. Policing city streets and physical locations is nothing like policing technology. LEAs don't see a difference between a lock on a door and a cryptographic lock on a cellphone. They can get a warrant to unlock the door, or worse just kick it in. Even if they did get a warrant to unlock a phone, if there is no key they cannot "kick" the door in (unless the use some other exploits), so they are demanding a key to every lock.