The performance and relatively light weight of the ef 24-70mm f/2.8L II is just so outstanding, so decisive, that giving up 4mm on the wide end, while adding 1.8 x the weight, plus about $1500 USD in cost, just doesn't seem immediately appealing.
On the other hand, Canon hasn't had a spectacular fast-50mm...ever? For all the talk of magic in the ef 50mm f/1.2L, after looking through hundreds of images on the web, talking with high-end pro wedding photographers, and seeing, clearly, the focus shift issues it has in well done youtube videos, I can understand why it has been a "love-hate" kind of lens. Any praise has been balanced with significant criticism. And not just for the focus shift. Even with spot on AF, at wide apertures it is soft. CA rears its head. And the bokeh, while at times impressive, also can look quite ordinary or even jittery. (I think part of the reason for unpleasant bokeh can be over-application of universal sharpening to compensate for soft focus on the subjects.)
In short, the 24-70mm does great in its slot, so not a lot of photographers have been thinking, "Gee, why don't they make it one stop faster, a whole lot heavier, a little tighter on the wide end, and almost twice as expensive?" But those of us craving a superstar 50mm f/1.2 have been thinking about it for years and are happy one is finally here. Even if it is a whole lot heavier and twice as expensive!