Does Microsoft promote people into Windows/Office executive positions more or less permanently, or does it rotate people in and out of those jobs so that nobody is wed to the success of those products permanently?
If those were the jobs people strived for and then hung onto, it's easy to see how the most ambitions people would work to get into those jobs and then use their skills (political and otherwise) to maintain those products pre-eminence and power to keep those jobs and suppress disruptive technologies that might displace them.
If those products were seen as self-sustaining and needing only slight guidance, then maybe Microsoft could have kept merely average people in those positions and/or made them less lucrative to push more ambitions and talented people into other areas of the company that could have benefitted from more aggressive and ambitious people who could have furthered more innovative stuff.
My guess is that Windows & Office were seen as the jewels and where the "best" people went, where they got fat and rich and did everything to suppress anything which might disrupt their fortunes. It almost sounds like the politics of Rome or the kind of thing that cripples an aristocratic society over time by preventing disruptions and innovations that would topple the established order.
Maybe someday we'll read a "Rise & Fall of the Microsoft Empire" that portrays Gates as Augustus and Ballmer as Nero or Commodus.