Apple Arcade (and similar programs like the Xbox Game Pass) pays developers to feature their games, often with a guaranteed payout which derisks the increasingly-risky process of game development, and for indie developers specifically this payment can be more than what the game would make if released naturally.

Otherwise, games are normal apps.

It is hard to make and market a game.

Apple Arcade is a system where Apple helps as a "Producer", and then you get part of the subscription revenue from people who pay for the Apple Arcade subscription and then play your game.