That optional GPG/PGP private key storage was also re-hidden (and almost but not quite removed) functionality by Keybase over the course of the application's life as they moved away from using traditional GPG/PGP-style keys to a more complicated but more secure system based on device-specific keys (and chains/webs of those keys and their derivatives), around when you needed another device to onboard the next device rather than just needing to sign in with username/password.
