Actually, Petty made a ton of money last year.
http://www.forbes.com/pictures/eeel45ehmg/the-worlds-25-highest-paid-musicians#content
16. Tom Petty & The Heartbreakers ($38 million)
Some acts seem to have an infinite shelf life on the road, and Tom Petty is one of them—the bulk of the band’s annual take comes from 46 dates over the past 12 months.
Perhaps still finding enough suckers to hear him playing the bars and casinos, but hasn’t headlined a big arena or had a to 20 hit in at least 20 years.