There are several articles that mention the lack of diversity on network television. It is noticable on more shows and networks than others, the CW which was a merger of the WB and UPN who each used black sitcoms to build an audience and then all of sudden cut them all from the schedule. The networks attracted an audience and advertising dollars and then dumped the black shows when they were no longer needed.


http://www.huffingtonpost.com/2008/12/18/network-tv-diversity-lack_n_151991.html



http://blogs.tampabay.com/media/2010/07/opposition-to-lack-of-diversity-in-cable-news-growing.html