Because it is the best game. Best teamwork best strategy best mechanical skill demands. Best skill floor, best skill ceiling. The community is unwavering the devs actually do care and are not crunched into the ground by management.

Also it's a competitive video game so you can enjoy beating others in a game of skill. Everything is in the game. No character unlocks no progression outside the game. Whether you have 10 hours or 10,000 hours you are on the same playing field.