As has been alluded to by others, perhaps some of this boils down to a mis-interpretation of the word 'dress' somewhere along the line, wayy back when the mills were just starting to label these patterns?

dress = women's garment (skirt, arisaid, and/or similar/unbifurcated garments)

vs

dress = formal

I would posit that the term was intended to mean 'formal' when applied to tartan for male wearers. Due to the vagaries of the English language, this was misinterpreted at some point, which is how we come to the discussion we are having now.

Or, maybe I'm just barking up the wrong tree, in which case I'll retire from the discussion.