I think its probably just down to the balance of accessiblity to start but devotion required to keep playing, in combination with the very intense monitization that gets put into production and marketing. For comparison:

Something like CS is far more accessible, but has a much larger portion of casual players and has Valve’s laissez-faire development/marketing. Valorant is is like CS but even more casual. Dota breeds far more devoted players, but the game is so complex it can’t grow, and again, has neither the high production value nor the marketing because Valve. There are games like Fortnite that can compete in scale, but the nature of the game and the focus on fun content over competitve integrity mean that the tournaments are more marketing events than measures of skill.