The cost of advertising is dependent upon the demographic and the size of the audience at a given time Advertisers demand a consistent audience. Radio must deliver that audience. Radio must cater to its audience.
Radio is the least socially responsible of the mediums, with the possible exception of film.
When radio was invented newspapers fought to keep it down. Radio and the film industry, fought to keep television down. Cable fought satellite. Mediums learned that other mediums were complementary. Broad casting the largest audience possible, no matter who the audience is made up of.