My first guess
Intel included PowerVR GPUs and hardware codecs sourced from Imagination Technologies (IT) in these chips. Ever proprietary and secretive, Microsoft and Intel probably don't have either the IP nor the necessary code to provide the updates. IT is now on the rocks after Apple decided they don't want to deal with this BS any more and yanked it from the iPhone and iPad.
Linux drivers were always reverse engineered, don't have proprietary IP and so, will continue to work. The same criticism about these drivers originally (lack of mfr secrets limit performance) now becomes a strength.
Long story short: lack of foresight.