The main answer is because it is against US geostrategic interests to provide a valid, informed, expert counter-argument - such as Finkeslstein can uniquely provide - to the pro-Israel narrative that dominates the state-level US discourse.

The less chartible answer is that Norman Finkelstein is a long-winded, horrible interviewee/guest. He does neither himself nor his message any favors by not learning to provide concise answers to questions, and engage in a "give and take" during interviews rather than providing a 20 minute answer to every question.

I love his depth of knowledge and unique expertise on all points about the Palestinian situation. But I have to listen to him at 2x or I just want to shut off the audio because every. single. answer. becomes a long-ass monologue and/or a book-reading on some tangential point. It is infruritating.

You have to listen to 4 hours of Finkelstein to get the information a better communicator could provide in 30 minutes. Not everyone has 4 hours.

Main stream cable news shows have 3-6 minute interviews. Finkelstein wouldn't even finish his first grievance story before time would be up. I can imagine he has been invited a few times, couldn't deliver a decent response in the time alloted, and the spots were never aired. Word got around and that is where things stand now. I'm not saying that is how it is, I'm just saying that is a plausible situation.

Right or wrong, you need to be able to have "elevator pitch" responses to difficult questions. Until Finkelstein can learn to do that, he will always be marginalized.