Fortnite is the most popular game out right now, so kids/adults are grinding that game like crazy because the game is really good at giving players the sense of achievement even when they don't win. There are bright colors, cartoons, dance emotes, challenges, events, all the dopamine traps are there. In general, kids/adults can be addicted to any game. A ton of people played Minecraft when it was released. What makes fornite so different is that it's free, and the whole battle royale concept is wildly popular. Fornite developers executed the game very well, but in my opinion I don't find it to be that interesting.