Jim, this is just my take. FWIW.
The great old breeders who made, tweaked, preserved, improved, showed, cared for, and handed down these birds were unique individuals. Yes, they read the same standard you and I still read, but each was an individual artist at work.
In short, they're different because of the different inner vision and work of great folks who came before us. They were different folks who took the birds to a place they wanted.
Or what Fred said ;-)