I think because they don't make as good a television personality as the radical name-it-claim-it prosperity preachers. They dress flashy, jump around, work up the audience emotionally. It makes for great television. Just having a guy stand there and preach the word isn't as interesting to as wide an audience.
One of the best pastors I know, weighs 300 pounds, speaks from God's word and has a small congregation. He Is a true man of God, who just needs prayers like the rest of those who we have in our pulpits.