The vast majority of games are sold over Steam. It's so overwhelmingly dominant that it eclipses almost every other platform put together, with some exceptions for consoles and mobile. Even when it's targeted at these, Steam is such a powerful marketing/discovery channel for games.
When Steam says no AI, nobody does AI. It's not just no AI generated content, some argue it means no brainstorming dialogue via AI and so on. The game dev community selects for this. This means that alternative platforms like Itch tend to also lean towards anti-AI even if they could differentiate by allowing AI. Consoles tend to also build for PC and adopting AI would cost them too much.
Pro-AI people tend to move to other platforms like Play Store and App Store, and lately we're seeing more quality control ramp up on these.