why pay Plex extra for what Jellyfin can do for free since it is an open-source project?

One big reason for me is that I got Plex lifetime on sale for like 70 bucks and it comes with a discount on Tidal, something I already paid for. With the discount after about 1 year and 2 months I've gotten my Plex Pass value out of Tidal alone. Oh and the paid features for PlexAmp are also really nice to use for the point where I barely use the Tidal app anymore.