Town ball, semipro, industrial and low minors PCs are the same way. I've gotten killed on generic cards of these sorts.
Cyclical. Like everything else in the hobby. There was a surge of interest when people realized that they existed ("Eureka!"), then stuff came out of the woodworks and it cooled down.
For the future, who knows. Personally, I don't think you can go too wrong with MLB team and minors PCs with HOFers on them. Niche for sure but very interesting to the people in that niche.
Chief Bender and George Weiss