$20000 isn't a useful amount of money. If they are getting $20k/month they can think about hiring a developer to work full time on the project, but at their current donation levels they could hire a developer for maybe 3 weeks before they run dangerously low on money.
Remember, Jellyfin is a fork of Emby which was a fork of Plex - both those projects were open source and then went paid. After being burnt twice like that I think it is understandable why many Jellyfin developers have had enough of that and will reject anything that even slightly could be seen as going paid. So while hiring someone might be possible and in the best interest of Jellyfin in a different world, they cannot do that in this world without losing support.
Remember, Jellyfin is a fork of Emby which was a fork of Plex - both those projects were open source and then went paid. After being burnt twice like that I think it is understandable why many Jellyfin developers have had enough of that and will reject anything that even slightly could be seen as going paid. So while hiring someone might be possible and in the best interest of Jellyfin in a different world, they cannot do that in this world without losing support.