I suspect that it might be a dealer problem more than anything. I really haven't seen much in the way of flat ground Spydies or flat ground folders of any stripe at B&M knife dealers I've visited. Maybe one Military at one shop, but that is it.
In a way it is really dealers which are the primary customer of Spyderco. What they buy (directly or through a distributor) decides what gets produced and what stays in production. I bet a lot of dealers don't buy flatground at all, other than kitchen knives.
A dealer that knows how to pitch flatgrinds can probably sell them as easily as hollows or sabers. But I expect that most shops don't even have them, and most sales reps at knife shops aren't knife afis, they are just standard retail clerks selling widgets.
'd bet that with a model like the flatground Police, that dealers just didn't order it and the average customer never saw it.
I don't know if it would be worth the financial risk to Spyderco, but something like a full-flat ground Endura or Delica sprint would be an interesting market test to see if dealers bite. We may be too quick to blame the ELU for not being educated, but maybe it is the dealer that needs education.