Curious, why do you think all those great guests come to his podcasts? Wouldn't they politely decline if they thought he's not a very smart guy and a terrible host? I really think John Carmack, Mark Zuckerberg or Kevin Systrom don't need the publicity via his podcast, so what other reason would they heave?

He has a large audience and is anodyne enough to not matter as part of the interview. He may ask some dumb questions or say some dumb stuff, but he won’t be hostile.

It’s why someone may go on tv for a few minute spot, it’s good for getting your message out to a large audience despite the interviewer being in the way of that.

I'm guessing it's because of his massive reach towards a specific type of audience that may be somehow beneficial to them. It's most certainly not because of the profundity of the intellectual exchange they have on these podcasts.