[mschaef]

mikestew has some good points, but flashing back a bit further to 87/88 is also illustrative.

The original PC was released in 1981, followed in 1984 by the PC AT. One of the things the PC AT was supposed to do is bring multitasking and larger (>640K) RAM - mostly thanks to the 80286 processor. The trouble that there wasn't a mainstream OS that used all of the 80286's capabilities until OS/2 came out in 87/88. At that point in time, OS/2 was both the solution to some long-term problems in the PC space and the annointed successor to DOS by the IBM/Microsoft pair that led the PC market at the time.

For a whole range of reasons, OS/2 turned out to be expensive to buy/run and incompatible with most of the software people actually ran. The market therefore kept its momentum mostly behind DOS until August 1990's release of Microsoft Windows 3.0. Microsoft had an internal skunk works project that brought 80286-specific features to Windows, but in a way that was more compatible with DOS and cheaper than OS/2. (Despite some technical limitations.) That's when Microsoft took a risk, and pivoted away from IBM and OS/2 and towards a Microsoft Windows specific strategy. It paid off for them and the rest is history.