IIRC, Epic had (still has?) the source for UT4 available as they were trying to push community contributions, mostly on the playable content side but I'm fairly sure they had the core game there, based off what is now a very old branch of UE4. The telling thing to me is if there was a huge demand for it there was no significant effort to pick up the torch, or even do yet another 'spiritual successor'.

Eh, "boomer shooters" died along side with Halo and LAN parties. Minecraft was the final nail in the coffin.

The knack and knowledge of hosting a dedicated server required skills. If you could one click button host a Quake 3 Arena server or UT, there would still be sort of a crowd.

But not only that, if you were new: servers got toxic with the same grumpy players knowing every single trick in the map to one-shot kill you with a rail gun. It got frustrating playing the same bloody map each map change. "Oh yay, it's cs_office again" /s

The whole genre got stale and never has been successfully reignited. As Discord to TeamSpeak; same misfortune.

Fortnite killed Team Fortress, Overwatch killed Halo and Minecraft was the new digital lego. None of them required such a skill to play or host the game. It was refreshing for it's time.

Not forgetting it was the upcoming of a new crowd of folk and as generations go, the old cards topple.

Who hosted an BBS when the internet came to be?

IRC today is pretty much stuck in dinosaur country and XMPP/Jabber never got a product which then was further nailed shut by Google & Co.

It was epic fun for the era but it had a death bed waiting.