Not a bad choice... since Minecraft Java edition only supports desktops, they don't have to deal with the abysmal Vulkan drivers on mobile.
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)...
They use bgfx for bedrock edition.
On mobile 3rd party launchers use ANGLE to use EGL or Metal drivers.
Honestly pick between Vulkan and DX12 is very superficial.
But you can easily make Vulkan run on macOS. Not sure what would be the reason to use DX12 in the new project today given free choice of technology, especially when team comes from OpenGL.
A company as large as Microsoft has resources to do a lot of things, but you’re not borrowing resources from the Office team to help on this project.
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.