And UT3 was definitely not a great game by anyone's measure.
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.
When I was a kid playing Quake 3 I had different servers bookmarked, knew the players that ran the servers and the general crowd that hung around. Had friendships and rivalries.
Modern multiplayer you may as well be playing bots. There's no community.
They're just all single player focused.
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.
This tension has arguably been a contributing factor in the collapse of the ARC Raiders playerbase, with a huge population who joined primarily to shoot and loot the robots eventually confronting the realities of a pvpve game, and peacing out for good after getting shot in the back or ambushed too many times.
Sort of like how Nintendo had the Wii, a huge hit but then almost immediately started to flounder for growth ideas as they didn't understand why it worked so well.
UT4 was a tech demo.
This means that they not necessarily were all that great.
If that's the new player experience, you done fucked up. Making sure new players actually have fun is a critical part of the game's design. You can't just rely on "...and then new players will have to spend 50-60 hours getting demolished before they start having a good time."
Easing that transition could mean different things -- a campaign, skirmish mode vs bots, full-on PvE co-op mode, automatching that actually works, whatever -- but you do need something effective.
Bots can teach basics, but many of these games rely on abusing game mechanics in ways the developers didn't think of in development so it's impossible to teach. Or things are physically difficult to pull off.
Movement shooters especially have this problem because a core part of the game is abusing the movement system and abilities to out maneuver other players. You can explain the how, but executing it all automatically is a real skill that requires practice. I adore Titanfall 2. I sunk hundreds of hours into it. It's really something else when you get the movement down, it all happens so fast you can't think about it you just have to do it. There's no way to teach that with a tutorial, it's muscle memory and perseverance.
Titanfall 2 has all of these things, campaign, skirmish with bots and PvE, but the skill floor and ceiling is still brutal. Whether it failed or not is a question of how long you expected the game to last, but it still succumbed to the same fate. The more experienced players pulled the ladder up behind them and the matchmaker didn't have enough players to give everyone a fair match.