Single player maybe, but that's nothing compared to the likes of UT or Quake.
It's not the only thing going anymore, but also people have orders of magnitude more choices. That's the thing that's missing today. Nothing is "dead", there's just too much competition now.
Honestly the aforementioned games have had much more staying power than more recent multiplayer games. And they're mostly played by old men like me.
also shout out to banana shooter or straftat if you want a quick fix in a f2p game. it’s not really afpsy but pretty fast movement and wacky guns in both