Both Windows 9x and classic Mac OS were fundamentally missing features relative to the alternatives at the time, though-- especially classic Mac OS, which (as of OS 9) still lacked proper preemptive multitasking and protected memory (for those who don't remember that era, this was a huge disadvantage in terms of stability and reliability, even compared to 95/98/Me which were roughly contemporaneous).
Current-generation Windows doesn't really have any such flaws-- the underlying kernel seems to be pretty sound, the hardware driver ecosystem around it is the most complete and robust of any mainstream OS, and they seem to be showing now that they can adapt to developer demands without doing something drastic. There's no real compelling reason that I can see for Microsoft to make a transition to Linux (or BSD, if the GPL is too toxic).
Current-generation Windows doesn't really have any such flaws-- the underlying kernel seems to be pretty sound, the hardware driver ecosystem around it is the most complete and robust of any mainstream OS, and they seem to be showing now that they can adapt to developer demands without doing something drastic. There's no real compelling reason that I can see for Microsoft to make a transition to Linux (or BSD, if the GPL is too toxic).