A hot dog from national chain supermarkets hasn’t changed all that much. We are just more sophisticated about our choices today compared to 1960 and have a much better variety and better quality. Same with breads. I think as we lose our ethnicity heritage the name hot dog just displaced frankfurter over time. Frankfurter also over time has been shortened to franks as in beans and franks.
The regional and local independents were a different story. Now we know about choices throughout the country and independents have adopted and copied each other. There were a wealth of independent choices, but what was available in New York would have never been available in Iowa and vice versa in 1960. Different regions of the country also adopted different names for products that may have been very similar. Unless one was well traveled in 1960 one would never know. Also, in 1960, the only way information was distributed with any timeliness and mass coverage was through official media and not the way it is now through the internet via individuals.
That’s my take. I also assumed a frankfurter was nothing but a hot dog as an interchangeable word in 1960.