Directly from GTA's website: "The overall program is expected to take approximately seven months to complete." During these seven months, you log 522 hours of flight time. As a CFI, you can log significantly more hours in the same amount of time, and get paid to do it. With GTA, you're paying for the flight time, room & board, and "required uniforms." Plus, if you go the instruction route, you'll have had experience as a commercial pilot- airlines like that.
Maybe it's because I've actually spent time instructing, and might go do some more, but I take issue with people buying themselves a job.