If the software makes money because it's expected to work reliably, every edge case matters. Web games aren't exempt from engineering challenges. In fact, the more trivial the problem seems on the surface, the more likely it is to have edge cases.
Bugs are always prioritized based on how big of a deal it is for the customer. They don't like to wait and they rarely give second chances.
AI doesn't fit into any dev workflow except greenfield or analysis. Everything else needs a lot of close human attention and human discussion. AI doesn't read minds.
Ie you are making the mistake of assuming the tech is static when it most assuredly is not
That difference is enough to unlock AI coding for so many real life teams
Why wouldn't a game dev do the same? It's pretty common for initial game releases to lack features.
A raytracer demo doesn't need to be engineered to the same standard as the Apollo onboard computer software. A $20 paint app doesn't need to work as reliably as banking software that handles millions of dollars of transfers every day. All software exists on a scale from trivial to critical. It's like saying a toy drone needs to be designed the same way as a F-16.