My guess is they want to try to get some fraction of these signups to try Peertracks. Perhaps they hope to create some relationship between artists and their fans. Last time I read about Peertracks it seemed to be talking about artists will sell shares to their fans. Fans become investors in musicians.
http://peertracks.com/Steemit has literally nothing to do with peertracks afaik. Different team, different code, different target market.