John Krasinski explained why he sold his web series "Some Good News" to CBS after he wrapped up 8 episodes.
In summary, he said it wasn't about the money, but rather that he needed to get back to his normal job and that the decision was to either scrap it or sell it off to someone who he thought would do a good job with it.
But again, not about the money...
Here he is telling his friend Dwight...err, Rainn Wilson about the decision. Skip to 12:45.