The basis for this is the overall sharpness wide open (though stop down the 56mm to f/2 and it's comparable), more flattering focal length, and better close focusing.

Cropping helps with some things, but good ole fashioned focal lengths help with conveying depth, or in this case slightly compressing it.

is a great portrait focal length.

I like this focal length for portraits, although it puts quite a bit of distance between me and the subject.

The 56mm f/1.2 has a greater minimum focal length.