It can be anything. The artist gets caught on TMZ saying something bad, his record gets dropped. Just like that. It can be bad research. It can be that a song has been on the chart too long. Perhaps they need to make room for a hotter song. All kinds of reasons. The main thing is it happens in collaboration with the label's promo team. Perhaps the label is backing off one single, and redirecting its priority to another artist. As I said, it can be anything.
Most commercial stations don't collaborate on most adds and drops with the labels. The labels are, to be polite, pests.
There may be some cooperation based on promotional opportunities, but we generally don't follow the label's playbook. If a song is still testing very high, the new single will just have to wait... or it will get minimal airplay.
My extreme case was at LA's #1 station where a song tested "power" for just over 13 months. In the meantime, we did not cut it from power rotation and did not look for a new song by the same artist, despite the record promoter's push.
In another case, same market, the first single from a big artist was not liked by the PD. She selected a different cut. The label had a fit, even calling the manager. It turned out to be the group's biggest hit ever, but the label's promo staff did not like it and had an ego issue in flipping to a different cut.
In any case, I think tall_guy was specifically looking at how research determines play, exclusive of outside influences.
I'll mention again the phone message of the PD of Power in LA when it was the top young adult station "Hi, you've reached the Program Director of Power 106. If you are promoting a record, you can hang up now". In the lobby there was a box for new releases. Promoters could meet with the PD one day a week for 15 minutes.