With those slower drives, programmers tended to be more careful about not wasting those preciously expensive I/O's - they had to put more care into architecture, often resulting in more optimized, efficient code. And since lags were expected, they handled waits more elegantly - hence the hourglasses and such. This immediate feedback even when there was a delay is what made the experience feel more responsive.

Modern apps that ship with browser engines just to show some UI are hugely bloated by comparison.

You also didn't have dozens of different telemetry, update, crash collection etc. services constantly running in the background eating up resources and I/O's. Go into Event Viewer, Services, and Scheduled Tasks on a pre-Win7 era workstation and you see how much less crowded it is.