Why didn't the Atari ST succeed?

image: Atari ad from 198A

As an Amiga kid, the title of William Blair's What's so great about the Atari ST? gave me a chuckle: I expected to think "that's what everyone asked themselves in 1989!" But I come away struck by how odd it was that the Atari 520ST didn't do so well in the years before Commodore put out the competitive A500. The 520ST was half t…