I'm guessing previously they indexed the data and didn't actually use it. Nowadays they're using it directly themselves. You could argue previously they were making money from Google ads but google was always ad free I believe. Results had sponsors for sure but that wasn't linked to your data
Plex is a far better and user friendly version than jellyfin or emby in my experience especially if you want to share to friends. Granted it's not open source and has gone commercial route so there is the risk it will continue there. But for now I wouldn't push to move. If jellyfin can get some more app support and continue to develop and be ready for when Plex messes up then it will take off.