Perhaps it's their culture of letting engineers experiment with stuff during work hours that also led to Gmail, Maps, etc. and the mobile game ad market is certainly big.
I guess this mainly competes with mobile games, most of which are mediocre at best and aim to get a few "whale users" to spend inordinate amounts of money on coins, gems, or whatever in-game currency.
Maybe the theory is that those games are so easy to vibe-code that completely democratizing it will lead to enough of a flood of games?
And a few will stand out and become Candy Crush-sized successes?
Or perhaps it's the idea that if you can have millions of extremely niche games, each may have a few hardcore fans because it caters to their specific interests (the same way Kindle Direct Publishing enabled hyper-niche literary genres)