Did the book have no answer? Status (in drug dealers' circles, the gangster/thug is higher status than a fast food job), more independent lifestyle hours (no 9-5), and seeing a way to move up (a la become Scarface) that culture doesn't portray from a "dead end" McD's job.
that's correct. they speculated -- they're economists, not sociologists -- that it was about status, hours, lifestyle, and the get-rich hail-mary long-shot potential.
workin McDs or Kinkos is eating shit every day, wearing a uniform, etc. and is fundamentally emasculating when compared to gang culture.