"the kids who grew up with live service" didn't really grow up with "live service", this is a misnomer. They grew up with a live service game, because it's not feasible to play more than one of these over any amount of time. They aren't "fans of live service", they are fans of Valorant, or Fortnite, or PUBG, or GTAO, or what have you. Maybe they dabble in others, maybe they switch at some point, but they switch because their friends switch, there's social elements at play here. Even if they like Valorant more if their friends are playing CS they will play CS as long as they have those friends.
This paragraph has multiple illogical statements in it.
First, I've never met a multiplayer gamer who has only played one multiplayer game in my life. We all float from GAAS title to GAAS title, just as SP gamers float from SP game to SP game. The only difference is that we stick with games longer than you. Everyone reading this right now knows they could walk into any high school and find a ton of kids who played Fortnite, Roblox, Minecraft, and Warzone etc...
Secondly, you suggest that maybe GAAS gamers switch because their friends switch. Why would this matter? Why does Epic Games care that more players are playing Fortnite today because gamers got their friends to play? All that matters is player preferences and what they're willing to spend their money on.
Also, and I have said this before, I am not sure you understand people that well. MP games existed before live service.
MP is not Live Service. The MP games of the past were mostly based on the old economic model. Pay once up front, and we don't care how much you play. The new model has a focus on keeping players engaged. That is a huge fundamental advantage of Live Service. An advantage that wasn't widespread before 2017.
A lot of us played a lot of it, going back to the late 1990s on PC.
PC was a relatively small market in the 1990s. The bulk of industry investment was spent on SP games using the old pay before you play model. Live Service is the next evolution of the medium.
But MP starts to lose its appeal over the years. It also becomes increasingly difficult to keep up with the userbase as life takes over. I would be surprised if the same people grinding season passes in whatever game at 25 are still doing it at 45 when they have a full time career, house, family. Life just doesn't work that way.
You've probably never considered Fortnites growth before. The game is significantly more popular today than when it was during 2018s zietgeist. The reason why it's more popular today is because the ratio of SP gamers to MP gamers has shifted drastically since then. Old gamers who prefer SP games are leaving the medium. New gamers who enter the medium are choosing Live Service over SP games.
At some point spending the little time in a game you control entirely has more of an appeal to it. If anything, games that want to hold on to those people will have to casualize, which will change their appeal, which is exactly what happened to WOW over the decades. WOW is basically a game you can bop in and out of and do whatever you want without much resistance, nothing like it used to be, and nothing at all like a competitive live service sweatfest game.
I don't think you realize the metamorphosis that's occurring in MP space. The old multiplayer games relied on the competitive "sports" model. Unreal Tournament, StarCraft, Overwatch etc... These games were highly competitive, relied in twitch reflexes, and often has very short gameplay loops akin to basketball or football. Multiplayer is beginning to boom because the technology has now gotten to the point where it can explore the "heroes journey" formula that the SP market once had a monopoly on. Multiplayer is now about larger worlds, a higher degree of interactivity, more social in nature, and giving players a variety of goals that appeal to their personality type. Fortnite, Valheim, Lethal Company, Among Us represent multiplayers new stage and the stage has only just begun.
It made sense that older gamers "aged out" of Unreal Tournament at a certain rate. The new model of multiplayer will continue improving at keeping the older gamer especially with how many kids prefer Live Service multiplayer over SP.