Well, Microsoft was interested in making it easy to develop Windows applications, and also in making it easy and pleasant to use Windows applications. They had reason to invest in learning how that could be done and in writing utilities that would let you benefit from their knowledge; doing that made more money for them.

Browsers are different. They don't really benefit from being written for, or from being used. This seems like enough to explain the difference. They provide some functionality, and giving your users a good experience is your problem, not theirs.

I feel like I've seen complaints that Apple has forgotten things it already knew about how to design a usable interface; that wouldn't be explained by this model.