Plex is in control of their user’s computing in a way Jellyfin isn’t. You can remove anti-features from Jellyfin software and even redistribute it. So it’s much less likely they would do something like Plex and it even doesn’t matter if they did as you can find others to work on it in a way you want. Plex is proprietary software, Jellyfin is software freedom.

Although Plex is running on your server it isn’t there to do what you want… unless Plex’s real owner permits it.

That’s how proprietary software works.