This policy allows Intel to clean up the x86 architecture
Intel's and Microsoft's dependence on each other has had a significant negative effect on the performance of their respective products. In Microsoft's case they introduced a lot of x86 specific dependencies into Windows which made sense at the time they did them but in the long run made it very difficult to port Windows to other architectures. When they did the ARM port they cleaned up that mess so WIn10 is now much cleaner than older versions of Windows. On Intel's side they've had to maintain backward's compatibility to every generation of MS OSes. As a result modern Intel processors carry around a lot of obsolete instructions and memory management modes that should have been removed years ago. With Microsoft enforcing a policy that only Win10 is supported on Kaby Lakes and beyond Intel is now free to do a much needed spring cleaning on their architecture.