>>724784407 (OP)
Because it's always ever changing and fun that applies to all ages. Especially once they expanded upon the game starting with zero build. Like, I'm 36 so the past year has just been like "here enjoy all your childhood fandoms on the map" meanwhile they are cramming in modern stuff like kpop demon hunters with fun game modes, custom maps are a thing which a lot of modern shooters ruined. The core game is built on unreal which is basically the best fps engine. There's all kinds of reasons why it's still popular and will probably continue to be popular.
Also it's easy to jump into have a fun intense round then go back to the rest of your life. I do the same thing with CS2 but a match in CS2 even with the newer shorter win requirement is still like 30-60 mins dedicated time. I can hop in fortnite and play a whole round and at maximum it's like 20-25 minutes for the storm to consume and it never needs to in casual zero build and most of the time you're done in like 10 minutes.