1- They do not shoot those TV series with film. They shoot with HD, which is pretty close to DigiBeta (which they used for so long time). So you can't blame them for not using RED, because shooting with RED is more difficult and costs more than HD. It's a fact that a lot of series do not have enough budget..
2- Most directors are from video background. They are comfortable with the idea of WYSIWYG. When it comes to RED they have to develop new skills to deal with focus, exposure, lenses RAW etc, which is not always an easy thing to do.
3- You can't easily get good CC people. This means that you can't pull out the proper beauty of "raw". With HD cameras the first CC is done on set. With RED you have to do it in post..
4- It's not easy to find crew who know to use RED properly.
5- Many of them believe that RED is not stable, especially in hot conditions. You know Gulf area is a very hot one at summer. Most people are surprised when I tell them that we don't have problems with our RED even in summer.