because even though Stewart has gotten to be a bit of a head case himself now, he is at least interested who he is interviewing and what they are saying. For the typical Cable or Network news interviewer, that's way down the list below
their career ambitions
their own political agenda
the agenda for the show rating
the agenda in the memo from the corporate brass
the hope to be able to put a 'gotcha' moment on their resume.
You have to have a foundational interest in your subject - view the interview as more than just a means to your own ends, for any interview to ever get off the ground and that's completely missing in just about all of today's talking heads. Until the interviewee senses the interviewer seriously wants to know and understand and begins to respond to that, it just stays adversarial and guarded and all you will get are talking points.