The fact that you went to MIT is probably the reason you aren't getting admitted.
Why would that matter? They have your money either way, and op has an additional MIT degree, which I would imagine would only help one during a job search, likely boosting GA's placement rate stats.
It's actually quite hard for instructors to deal with classrooms with very uneven advantages between students. Given that these courses try to get the most of such short time periods, I'd imagine you'd either be unhappy with the pace or perhaps lead other students to feel like they're lost.