That has always been the case, it is mostly FOSS circles that argue about APIs.

Game developers create a RHI (rendering hardware interface) like discussed on the article, and go on with game development.

Because the greatest innovation thus far has been ray tracing and mesh shaders, and still they are largely ignored, so why keep on pushing forward?

I disagree that ray tracing and mesh shaders are largely ignored - at least within AAA game engines they are leaned on quite a lot. Particularly ray tracing.

Game engines aren't games, or sales.

Both-ish.

Yes, the centralization of engines to Unreal, Unity, etc makes it so there’s less interest in pushing the boundaries, they are still pushed just on the GPU side.

From a CPU API perspective, it’s very close to just plain old buffer mapping and go. We would need a hardware shift that would add something more to the pipeline than what we currently do. Like when tesselation shaders came about from geometry shader practices.

The frontier of graphics APIs might be the consoles and they don't get a bump until the hardware gets a bump and the console hardware is a little bit behind.