Same way it always has, the labels pay for it. And these days there’s even less DJ decision involved, most big radio stations buy computers that do their programming. They tell the computer what kind of station they are and the rotation gets set by the computer, the DJs job is to talk about what the computer says they should during the times when “DJ talks” shows up on the list. Few and far between are the DJs that even a little bit of input on their playlist anymore. Assuming there even is a local DJ anymore, a lot of the computers come with “canned” DJs.
Nowadays all the radio stations are owned by Clear Channel, anyway.