There was no particular reason not to tack an unarmed damage ribbon on to the improvised weapon fighter, except that it apparently seriously confused some people into thinking the subclass was supposed to support unarmed fighting as a first-class option (despite there already being an entire...
Yeah, see, if you're talking about the Brawler as the "unarmed damage fighter", rather than "the improvised weapons fighter with an unarmed ribbon", then you are in fact confirming that the core issue was people not understanding its niche.
For the curious, Planescape made #129 on the October 25th USA Today's Best-Selling Books list (for sales from Monday the 15th through Sunday the 22nd), the first D&D release to make the weekly 150 best-sellers list this year.