When people may get into a competitive game, data shows that they commit to it as their primary game.

It becomes a part of their identity. You see things like Leage of Legends going strong despite a slow down in new players - people just commit to it for better or for worse, likely because most of the skills they’ve gained in it and friends they’ve made will not transfer to other games. Even other FPS games have different nuances that are non trivial once a player becomes serious about winning.

Take Wild Rift vs Mobile Legends Bang Bang. MLBB is objectively a worse rip off of League of Legends and the Chinese game Glory of Kings, but it was first to market on mobile. Now that League has released their mobile version with immense polish and quality, many mobile moba gamers just aren’t interested - they’re already totally invested in their main game, despite it being proved in court that it’s a cheap copy. (Not cheap as in $$$ though)

When you’re a kid, spending time on any competitive game will be fun (if you can handle the baseline toxicity) since you will start bad at most of them. When you get older there is a real cost to switching, you will not have as much fun until you build up the years of muscle memory that would be needed to even approach your skill at the previous game.

Because of the lock in, if a competitive game finds a sizeable enough player base and lasts a good handful of years, the devs essentially get free rein to milk their cow as they see fit.