Canon produces EF-s lenses that mostly are rated lower than L lenses. Canon supplies these lenses with crop cameras with a equivalent of 40+ MP on full frame cameras. So they do think their lenses already are good enough or they must believe crop camera buyers are not critical to lens resolution.
Personally I believe a lot of complaints about image quality relate more to user error, that become visible when a sensor captures more detail, than to really poor lens quality. (I am a pixel peeper and use "old" L lenses and I am satisfied with the result. I see no problem with a 40+ MP camera for me.)