Where are you getting monopoly from? Large game franchises that have launched (or become popular) in the last decade or so all started from small, independent studios, or even just a couple people modding an existing game. DotA and PUGB are big, started as mods, and have spawned (or at least popularized) entire new genres. Valve has a history of buying popular mods and turning them into franchises (TF, CS, Portal), and they pay exceptionally-well. Minecraft exploded from a one-man endeavor to a gaming behemoth.

Successful games tend to get purchased by larger companies, but there are a lot of large game companies. Valve, Epic, EA, Nintendo, Sony, Rockstar, Activision Blizzard, Ubisoft, Bioware, etc. And that's not even getting into mobile/Facebook games, which are easy to speak derisively about, but are still major players in the game space.

Game companies are about the most-diverse and least-monopolistic of all media we consume.