Though I thought a company large as Microsoft would have the resources to build a cross-platform RHI with the most stable API available for each platform (DX12 for Windows and Metal for macOS)...
The relevant measurement is the resources Mojang has as a studio. And I expect the decision here is that they don’t want to commit to the long term maintenance of three renderer implementations on the Java side.
Another concern is that modding is a major part of why Java Edition is so popular, and that includes shaders specifically. This is already going to cause chaos in the modding world as it is, no need to compound that by making shader mods that much more burdensome to maintain.
The main thread is often the limiting factor in minecraft. Minecraft just can't go as fast as the GPU could render the scene and even with quite a lot of shaders things are CPU bottlenecked. Hopefully this changes with time as modding minecraft could certainly do with a bit more CPU time free.
There is the non-Java version (Bedrock), but that’s not nearly as extensible.
Now both exist and get roughly the same feature set now, but the Java version remains popular given the vast variety of mods and servers.
There’s a native version called bedrock
https://en.wikipedia.org/wiki/Microsoft_Java_Virtual_Machine