In watching this video, you can hear the motivation of Chris Hardwick of the Nerdist podcast (who gets about 4 million downloads a month). He started it because it was something he would have control over.
He talks about how our society is so niche oriented now, “You don't need 30 million people to listen to your podcast. If 10,000 people listen to your podcast, which is not a hard number to achieve, then 10,000 people are listening, and you can build a community, and literally change the world just recording into a microphone.”
He talks about using Free items such as Audacity, or Garageband to assemble your podcast and states, “There's no excuse — other than you don't want to do it — why you can't do a podcast now.”