MS cannot break legacy compatibility anytime soon even though I'm convined they actually wish they could. There is a huge amount of corporate applications that still rely on legacy WinAPI and these applications usually cannot be easily fixed. There are applications out there whose lifecycle is "Developed by A which was a branch of B, B was taken over by C, C went bankrupt and sold to pieces so the original app is now owned by D." There is a good chance that by the time D owns the app, it's source has become a hardly maintainable mess nobody from the D company actually understands.
Windows division of MS makes money by selling new version of Windows. If you take in account how hard if was for MS to make people move away from XP, you can probably imagine that convincing people to switch to a Windows version with limited (or none) support for legacy apps would be next to impossible.
Apple can do whatever they want because their userbase is much smaller and there aren't many huge industries that rely on MacOS.