If I had to guess there's a couple reasons:
1)Quality-making a good game requires extreme attention to detail all of which is non coding related. The animations on idle characters, how the background characters look, the sound design and clever story. 90% of gaming is art
2) backlash from players. I think this is an important factor but not the dominant factor. For reasons like games like Slotbound have had amazing positive responses despite being ai generated as long as they are high quality. On the flip side reputation does matter for major studios so adoption can be slow.
3)No money in the industry. Most game studios aren't raining in money, therefore making video games would be an expensive and time consuming hobby that got slightly easier, but is still difficult. A normal prosumer simply doesn't have the time nor dedication to make an project that is going to take months of their time
These are my guesses, but I would love to hear responses from people in the industry or people who have attempted this idea or VCs who have their own thesis on the market.
p.s. this isn't a lazy attempt startup research, I'm seriously just curious