It was movie studios convincing microsoft to ban from Windows the best featuresof SBlaster cards (those features are STILL banned by the way) because they were afraid of people using them to pirate movies.
It is a reaaaaally long story, but to make it short: MS changed radically how windows drivers worked, and what a driver could do, during the transition to DVDs, it killed sound cards (because no more advanced 3D sound rendering that sound blaster could do), CRTs (no more funky resolutions, no more overlay mode, and other fancy CRT features), and initiated the slow death of VGA (that also happened for other reasons but this contributed a lot).