That was untrue even then. Even if no individual userspace program was multi-threaded or multiprocess, you still get a benefit from being able to run multiple programs at the same time (and not just time-shared on a single core).

I don't know about that, single core computers weren't known to be used in a multitasking kinda way. You usually had one main program open at any given time. It's not like my computer with a Packer box running on the left, a code editor in the middle, and Hacker New + 10 tabs on the right.

It was Word.

Or it was 3D Pinball.

The issue was Word and 3D Pinball didn't use multi-cores well and some people didn't see anything to gain. They thought "well it isn't going to make lag in Word disappear, or Pinball more fun." They completely missed that they could run both at the same time now.