Because it's been remastered, essentially, from its original format and resolution. I'm sure that you could color "correct" it to a more modern state, but then you'd be the one doctoring it.
Hence "essentially", yep. It's been updated, whether by hand or by algorithm or both, and the finished result is a hybrid of old format & resolution and modern graphic standards.
So I did some research I to this and yeah, it might look like that but this image was lifted from the Getty image archive where they claim it is just a high res scan of the original medium format negative.
I suspect they applied some dust removal and maybe a contrast curve.
You'd be surprised how good some of these negatives can look after all this time, right?
The image itself was taken by a chap called Murray Garrett. He used to be Bob Hope's personal photographer, but shot loads of celebrities up until the late 60s.