I think it's because he welcomes everyone on the show, and just lets them talk. He's pro-gun but had a former Marine and cop explaining why guns are terrible, for example. He's also had Bernie Sanders on, and reaction to the video has been very good https://www.youtube.com/watch?v=2O-iLk1G_ng . Dr Cornell West is one of his personal heroes, had him on the show recently too.

At the end of the day, I suspect most of his audience is US-libertarian, right-wing though.