It lacks a tad bit of polish compared to Plex, but it can be run entirely offline (meaning without a centralized account like Plex). Plex player on Android TV was awful for even native streaming of 4k, where Jellyfin performs.
That's weird, I had a different experience: I definitely heard about Plex the most, but often in a negative light. The alternative presented (again, in my experience) was always Jellyfin.
It was easier to find forums for Emby than Jellyfin.
IDK, it was just an impression I got.