Price aside - the 1.4 has a number of other advantages also.
Weight, for one, it's more than twice as light as the 50L 1.2. Smaller also.
The 50L has all that big beautiful glass, but that heavy glass has another disadvantage - it's a little slower to focus.
Of course the 50L is 4x more expensive too, so there is that as well. But it's got that dreamy 1.2 vs the 1.4 of the smaller 50.
Nothing wrong with either. I think many people look at it in a linear fashion - L > non-L, but you shouldn't look at it like that. They are two similar, but also very different tools, you need to pick the right tool for the job. Wedding photography is run and gun, a split second can be the difference between getting the shot and having it come out soft. In a case like that I honestly would choose the 1.4 every time. Also you're on your feet and carrying gear so the weight is a huge advantage also. For more posed photography, studio work, etc, the 50L would be the best choice. L glass isn't always the best option just because it's the most expensive one. Right tool for the right job.