I suspect people are forgetting that Canon are in the business of lens manufacturing to make money, not to satisfy photographers economic needs.
Yes, and so are Canon's competitors. So how does that explain the fact that Sigma released a 50/1.4 under $1000 that is better than any Canon 50mm prime out there? I can assure you that Sigma wants to make money as much as Canon does. What's Canon's excuse for not offering a high quality fast aperture 50mm prime--something that is arguably the foundation for any 135 format system?
The current 50mm lineup is no more or less difficult to manufacture now than they were when they were designed. Production comes and goes in batches; when they want to adjust their manufacturing processes for a different optical design, it is not as if they are reinventing the entire lens from the drawing board. All of these lenses have been out so long they have long since recouped the development overhead and then some.
The bottom line is that Canon makes crappy 50mm primes. There is no escaping that. They do not satisfy the basic criteria of reasonable price, quality construction, fast aperture, and good sharpness. No, I am not demanding that they make an AF version of the Otus 55/1.4 and sell it for $25. I am saying that their existing 50mm lineup has been lacking for years, and I claim this is in large part due to their apparent interest these past several years in making cheap consumer zooms or disproportionately expensive L zooms and superteles. And so we have competitors like Sigma swooping in and eating their lunch.
Again, that's *SIGMA* we are talking about here. This the same lens company that used to make knockoff cr*p designs. If even THEY can design something like the 50/1.4 Art, then Canon has ZERO excuse not to do even better AND for less. Lens design is still difficult these days, but it is a lot more computer- and data-driven than it was even back when the 50/1.2L was designed. Had Canon done its homework in lens R&D, they wouldn't need years to make a competing product.
Oh, and for those of you fantasizing about an f/1.4 IS design--it's not going to happen. We will be insanely fortunate to just get ANY new f/1.4 design from Canon these days, much less one with IS. Canon's lens design philosophy these days is to slap IS on everything, reduce the aperture diameter, and call it a wash when it clearly isn't. They do this because it's cheaper to throw in IS than to design and manufacture for the much tighter tolerances of an extra few stops of light. It's easier and more profitable for Canon to make a lens that is sharp starting at f/4 rather than design a f/2 lens that is soft in the corners.