Dota 2

Apart from meta which has already been explained, players also play heroes which they're familiar with. So the saying goes - "I fear not the man who has practiced 10,000 kicks once, but I fear the man who has practiced one kick 10,000 times." Some players become synonymous with certain heroes because they become such dominant forces in the game when given those heroes. Pros will practice and get exceptionally good at a small pool of heroes rather than play all heroes at a mediocre level.