In the past, Northeastern has used NU.in to shield students with lower ACT/SAT scores from being averaged in with the rest. This strategy works since it doesn’t have to report the scores of incoming freshmen who aren’t on campus. It raises NU’s rankings, and gives a chance to full payers who wouldn’t normally get in.
Same reason why they don’t accept SAT scores from international applicants, who typically have trouble with the English section.
So, if you really want to get into NU.in, try lowering your SAT scores.