IMHO it’s in part because of what I assume are different business models between a game like GTA and many / most businesses where a website / web app is core to their product.

Different business models result in different environments in which to conduct software engineering; different constraints and requirements.

IMHO constant and unpredictable change (which I assume happens less for games like GTA) is one of the big differences, as is the relationship between application performance and profit.

But I like what you’re saying and would love to see that world.