Something interesting I've noticed over the years is that false teachers tend to rely much more on emotion and showmanship, which is better communicated through visual media or television. This is why TBN has been so successful and why Benn Hinn, Kenneth Copeland, Joyce Meyer, the gay Filipino guy, etc, all gravitate to TV.
On the other hand, the good preachers and teachers who's ministries center around teaching and preaching do not need to use visual means. Hence, the reason the good, sound preachers and teachers are more likely to be on radio or podcast, rather than television.
I think there may be a stewardship issue, as well, as radio costs so much less than television, and podcasts, virtually nothing.