The thing is, making your own game engine can be beneficial because a lot of engines are so general that you may lose a lot of performance benefits. We have seen this issue with how custom engines pushed the boundaries of games to a extreme, but when games moved to cookie cutter engines because it was cheaper (well, that has changed also), but in return they ran into issues with limitations on the engines or performance issues.

Now with LLMs the entire "make your own engine that is optimized for your game" is ironically back. But people like Blow balk at the idea that a LLM can make a game engine.