Nothing really, we played it for 120h and then moved on to other games. I assume many other players did as well. It's not a live service game with seasonal content and constant changes or updates. There are no leagues or leader boards so there is no reason to return to the game other than the occasional fun round with others.
But to be honest it's fine as it is, solid game play and nice maps. Not every game needs to run indefinitely and keep huge numbers of concurrent players. The devs did their thing, showed the world what games should be like and now they earned their retirement. If they come back with updates, good. If they decide to make another banger game, even better. But they don't have to, if every game is an endless time sink with seasons, battle passes, skins, mtx and fomo built in there would be no exceptional games like we had in the past years.
Also the game is highly dependent on the people you play with, the longer fps games run the better people usually get. Beginners or players with little time get pushed out because there are seasoned gamers that do nothing else than running the best meta weapon and learned all the maps. So for new players the fun declines and veterans keep complaining about the lack of new players.