DISCLAIMER: I understand the reasons for fast aperture lenses and their benefits. I play -to a certain extent- devils advocate.
I think the problem is that for many users the zooms are actually good enough these days, and in particular, the consumer zooms are damn fine for the money. Why do you need f2.8 or faster? Just up the ISO? Etc.
Personally, I shoot in low light (mostly clubs & outdoor events), and use ISO >1600 often. If I was a Rothschild, I would buy f/1.4 L primes. Not being one, I wish for cheaper & f/1.4 < aperture < f/2.8
If slow (as in f/3.5-5.6) zooms are optically as good as f/2.8 primes & ISO solves the speed issue, at some point people would just stop buying f/2.8 primes. I would think Canon would want to sell more lenses, but possibly might want free those resources to make lenses for more profitable EF[-S] / cinema / fill the blank lenses, or just close the production lines and save money.