I'm guessing all those shitty podcast networks (and they are all shitty, based on the product I've heard) are run by guys with egos, who don't want Tom coming in and displacing their existing number 1 flagship show (which they host themselves) and then them having no creative input to the now flagship show on their network.
As for radio, I'd bet it comes down to advertisers. The network, will want to have some degree of creative oversight due to the demands of their advertisers and/or they don't understand what's funny either.
So long story short, a paid DIY Best Show is good with me.