Without getting overly political, there was considerable pressure put on Nielsen to "give a break" to minority and women owned stations, particularly in the last few years.
The people running Nielsen have enormous daily contact with radio stations and radio groups and trade associations. But they also have to work with the MRC, which was created 65 years ago to prevent "bad practices" involving ratings. The MRC is particularly supported by advertisers and their agencies because they need a pricing metric.
Getting people to "vote" for your station destroys the pricing metric as you are trying to convert listeners into fans who fill in exaggerated or false listening to your station.
I'm a broadcaster, too. I built my first commercial station when I was 18 and have been at it for 66 years now.
Name me one of those stations that will get agency buys. The immense and almost total majority of those that don't subscribe but are minority / female owned don't "score" high enough to make any kind of agency buy. You own an agency, and should know that it is rare... to say the least... that a station with a 0.3 share (an example) gets on any buy (unless it is combo sold with some co-owned bigger stations as a bonus).