I have a password manager.
My parents do not.
They do have a Gmail account and know how to use Netflix, so they know how to use Plex.
I mean, that's not the dealbreaker, there are plenty of bigger issues with Jellyfin than not having a Google authentication integration. They definitely can log in with a password and do for other self-hosted services, but the fact is that Plex having the option does remove one annoyance from the process.