Because when a normal conservative appears on an MSM show he is there (a) to get his message out to a large cross-section of undecided voters and (b) he will be adversarial toward the received wisdom of the liberal media and press his conservative case.
When Ron Paul goes on the Alex Jones show he is not only addressing a limited audience of nutbags (an inoffensive move of itself) but he is encouraging and receptive to the nutbaggery of the crazy host and the host's crazy audience - he does not get into arguments with Jones or contradict him. Jones kisses his behind and he warmly humors Jones.
You're not going to see that kind of lovey-dovey interaction if Duncan Hunter was interviewed on Hardball.
Because Alex Jones thinks that Bush and the Jooos did 9/11 for oil and imperialism.
Don’t you think that constantly appearing on his show should disqualify one from being the GOP nominee?