The Topps negatives are transparencies. Transparencies were a big commercial medium in the pre-digital age until 35 mm slides more or less replaced them. Their main utility was the ability to drop them onto a light table and instantly see the true image, which is very useful for an art director or editor trying to select an image. Needless to say, it is an archaic technology. They are collected in other fields. Here is a Steve McQueen 4 x 5 transparency from a 1970s Academy Awards show:
As collectibles, I am not sure of the long-term viability. The ones I saw at the Topps booth at the National were showing some signs of degeneration. Film isn't that stable a medium. I have a few transparencies from the 1960s that are showing signs of degeneration. It also requires some careful storage in conditions that are not the same as cards for optimal lifespan.