I remember back in 1999 there was a Quake 2 bot that used neural networks to learn the game. It was never good enough to actually provide any kind of challenge for players, but it shows how long this stuff has been around. It’s just not used much because it’s quite a lot of effort and, in most shooters, the player won’t notice the difference. It also gives you less control over the difficulty curve of your game if the AI is changing as it goes along.