Three simple reasons:
* Timeshifting. In essence, this means that you choose what content you listen to when - something traditional radio delivery can't give you. Right now, I'm in the middle of reading a book, so most of my discretionary time is taken up with that. I'm not listening to many podcasts.. but am I missing anything? no! When I'm ready, I can pick up Dawn and Drew right where I left them - or, if I'd prefer, I can skip a few episodes and just catch up with the latest.
* Choice: Podcasting leverages the "long tail" possibilites that the Internet has made possible: instead of being limited to the 5 or 6 choices I have on broadcast radio in this geographic location, I can pick from any podcast anyone creates in the world - none are any harder to listen to.
* There is no third reason.
This post is a followup to an earlier post in which I took the contrary position.