My bet is the fact that most EF-S buyers buy the kit and could weld on the lens makes it hard to justify the development expense. The fact that the next-biggest group is likely the sports/ wildlife shooters who can use FF glass makes it even harder. The steady march downwards of the price of FF might just make it unviable - is the "step-up" purchase from a T7i going to be an 80D + 17-55 instead of a 6D2 (or RP) + 24-105? Yes I know there's a price difference there, but the smaller that price difference is, the fewer people who will be there to amortize the development cost across. The RP will in all likelihood get price cuts, and when a 24-105 3.5-6.3 is available as a kit...
That's a good point about EF-S owners and EF-S lenses, but it's also difficult to separate causation from correlation. Is it a lack of EF-S glass that leads Canon users to ignore the EF-S ecosystem or is it a lack of enthusiasm for the ecosystem that results in less glass being manufactured for it?
Fuji manufacture a lot of compelling crop glass, so clearly there's a market, but they cater to an upscale market and have the advantage of a smaller focal flange distance. I wonder how big a factor that is. Their fast wides look nice. If I were starting over, I suspect I'd start with Fuji.
Regardless, the RP seems to indicate that Canon's interest lies in affordable FF options, and why not? That caters to their strength, FF lenses. I'm more worried about the future of the M line....
And furthermore, the 24mm STM EF-S is #2 in Amazon's sales rank and the 40mm EF STM is #68... despite it being a useful focal length on both crop and FF. And I thought the 17-55mm IS f2.8 was a nice lens (I owned two of them).
I'm in the minority here, my primary dSLR body (selling my SL1 since it's not enough of an upgrade) is a Rebel XT. And I have, other than the kit lens, the 10-18mm STM, 18-35mm f1.8 Sigma, 50mm f1.8 STM, 24mm STM, 40mm STM, 85mm f1.8, 70-200mm f2.8 II IS, 4.5mm Sigma f2.8, and I'm selling my 55-250mm STM only because it's redundant with the 70-200, but it's a great lens.
And this is after selling a lot off. Canon definitely hooked me to the ecosystem with a crop body. (I did briefly upgrade to a 5D Mark III and loved it, but it was overkill for my needs.)
Edit: Amazon's sales ranks disagree with me. EF-S lenses seem to sell well.