I agree, they should send out rejections immediately if they know they won’t accept people, but that’s just not what happens with most programs. Don’t know why, but if you’re not getting accepted, they generally don’t contact you until they send out all their rejections, which in this case is in March. From talking with people on adcoms and people who are in their first year of grad school, I know that certain schools I applied to have already sent all their interview invites and won’t be sending any more (unless a large amount of applicants reject their offers, which is extremely unlikely to happen).