Howard Stern makes a risk-free $80M/year for 4 hours of radio 3 days a week. Maybe he could make that much making podcasts, but why risk it ? He's at the tail-end of his career anyway.

Do you know a lot of "smart" people who would trade a guaranteed $80M/year for possibly more doing podcasts ?

Stern is smart :) He obviously could do that but can't be bothered. He's not starving to death. So unless he's going to leverage his brand to build others and broaden his (a la Oprah) by having a family of stations under his control then it's probably not worth it to him. How can he not go to bed thinking, "I'm one of the luckiest schmucks in the world"?

The entire US podcast ad revenue in 2017 was $314 million. Stern is paid $80 million a year. Seems like the smarter choice.