The 'why not' is not from the perspective of the industry - it's from the perspective of the customer. Can you automate several tasks by using AI during game development? Sure. Will it translate into a better price or a better experience for the end-user? Let's see.

Let's say you give AI the unimportant tasks. You manage to reduce a lot of waste and maybe optimize your workflows. You improve efficiency. Maybe you can make more games in a shorter time span. Will you be willing to sell the games for less than the standard $60? I find this unlikely. This impacts me as a consumer - why don't I see a reduction in cost, if it now costs less? Why am I still paying the same price for something that your improved tools can make at a fraction of the cost? Didn't my previous purchases already give you enough money to invest in AI? Where is my benefit?

Let's say you give AI the big tasks - you make it write story, generate graphics or code. But AI's current level doesn't allow for originality, or even cohesive thought. You'll be churning out garbage until your AI is actual intelligence. This again impacts me as a consumer - why am I sponsoring your experiments with my money? Why am I paying the same for garbage as I would for quality content? Will you share your end-game profit with me? If I buy your first games to support your endeavor, do I get the next versions for free? No. I don't. I'm just wasting money on inferior products, and when they become superior - I will reap no benefits.

So - sure, let the companies throw themselves at this. But I'm not investing my own cash in their research.

No. Hence why it's a buzzword. The CEOs don't know how it works, just that it somehow reduces payroll. For AI to do what you want it to do, you have to train it on hundreds of thousands of relevant data points over many weeks/months/years. That takes manpower, and consequently, payroll.

Also, games are supposed to be art. An expression of the humans creating it. Automating the games industry would make any MBA grad jizz in their pants, but it's antithetical to the survival of the medium and, consequently, the industry. You want nothing but freemium games meant to milk kids of their parents money? Nothing but shitty mobile games and live services from now on then.