I think that this is because Intel's drivers are just Mesa drivers, and part of why that's possible in the first place is because Intel's not really competing w

I think that this is because Intel's drivers are just Mesa drivers, and part of why that's possible in the first place is because Intel's not really competing with AMD or Nvidia and don't make efforts to keep their designs secret... which means that Intel isn't duplicating work already done in Mesa, but building on top of it and making Mesa better.