Well yes, it might be a simple feature, but it's still work someone has to do, and there's many requested features - as well as maintaining the current feature set. I do expect Jellyfin to get this feature at some point, but it might take another 5 years.
As we're talking about existing/missing features: Sadly there's an internet connection required to login to Plex, which is a no-go for me.
And I'd really love a feature to be able to share my library with someone while being logged in the same account. I.e. a kind of federation without duplicating content. Iirc Plex has something like this, by keeping the Plex server and user account separate.