For a more level headed take :

Think about how complicated a game is. Enormously huge environments, behavior of npcs and objects fitting well defined rules, multiplayer synchronization.

So even with pretty advanced AI, getting A game that can be played is a very different ask from "give me a game like gta 5 but better"

Moreover, even if a machine could in fact give you a "better" knockoff of gta 5, without many people playing the game and giving the AI feedback on where to improve it still might not be a very good game.