And remember, back then the whole notion of a _personal_ PC was very new, and thus companies with first mover advantage got huge leverage by instilling the idea into common people that AT/XT "common phenotype clone" is the computer.

Lots of people then got an idea that a computer must be a kind of at/xt derivative and nothing else:

My parents brought a second hand CZ310 from Japan in late 1994. A super expensive machine even for them (they were possibly within the top 2000 at that time in Russia.) I remember, mom saying about those times affectionately that she asked for "the best computer the money can buy." And that when it gave up the ghost in 1997 or 1996, the repairman simply did not believe that it was a computer and not a some kind of a gaming console.

The failure of non-PC-clones in the 80s/90s is mostly attributable to those two deficiencies, I think.

Then again, both Atari and Amiga tried that with their 030 machines and had no success. They were not taken seriously as workstation vendors (in the then lucrative workstation market) in many cases because of the brand on the box. I distinctly remember a UnixWorld article about the Atari TT030 with the headline "Up from toyland" (above an otherwise positive review)