I wouldn’t call it subjective. The issues that it has are all objectively there, whether or not you’re bothered by them is what’s subjective. If you’re personally ok with all the quirks, bugs, missing features and general lack of polish that plague Jellyfin but not Plex more power to you. But those problems exist regardless, and they are the answer to the question you asked.

Of course it's subjective, but it was you who asked why people continue to use Plex. This is a reason, and the reason is valid whether you share the same experience or not.