Most Fifties doo-wop was recorded on small, independent labels that had only local or regional distribution. Result: a song could be Top 40 in New York and never be heard in, say, Atlanta, Houston or San Francisco. But, they could take a group of kids right off the street, record them the same day, and get (actually buy) airplay within a week.

After the "payola" investigations of 1959-60, most of the independent labels folded--they couldn't buy airplay anymore. The survivors all had national and even international distribution, had better-quality studios, improved marketing, etc. But they were a lot more selective in who they chose to record. Result: far fewer black singing groups made records.