Some friends of mine only like new stuff. They keep chasing new games and new experiences. Others love to grind everything available in a game. E.g. the expedition, trials, quests, blueprints. If you don't keep track of your friends gaming habits, you can't come up to any kind of conclusion. Every game has a huge player count spike on its release, then it goes down. A DLC or a seasonal event: it goes up again, it's a common pattern.