Jellyfin was forked from emby (emby is similar to Plex, jellyfin is open source) in 2018 when emby went closed source, and they implemented sync and remote streaming if I recall correctly.

It's a principle thing mostly. Plex just keeps ignoring features users want and trying to push some monetization model.

They regularly implement what I'd say most would consider anti features.

For example, I remember the push back on the mandatory "recommended" tab. It's the first thing you see when navigating to a library. Wow. Neat. Some bean counter at Plex is "recommending" what I should watch on my own library. No thanks.

There was also the fiasco with emailing your friends things you've been watching. Just what you want where you store all your legally owned DVDs with your legal streaming rights to your friends.

Then there was also a thing where they began collecting data on your media libraries to their servers.

There's also mandatory Internet connection if you want to have local users :). Lots of people barked at this and they ignored it and tried to spin it as an ok thing. You cannot have other people in your family have different watched status and stats without connecting to the internet. Oh did your Internet go down? So did Plex. At that point how's it different than Netflix. Not to mention we're the ones doing the hosting. It's in our network. This should not be reliant on an Internet connection.

The list goes on.

It works pretty well and I've thus far been too lazy to change, but jellyfin is open source, and doesn't have evil people behind it.