>>106183287 (OP)
When games started making real demands on hardware, and topping it off with offering a SVGA option, in the early- to mid-90s.
Up until then, most games were in mode-X VGA, which even a 386SX could hit 70 FPS (not 60) without problems.
Going by memory, Doom was probably the start of the slide, followed by games like NASCAR Racing, Descent and Slipstream 5000.