I assumed they pushed the deadline back so far to get as many apps as possible. I remember talking with admissions several months ago and I asked about how many applicants they receive/how many they accept; I can't remember the exact details but I think they were accepting about 60 per campus, and they got 120 apps for each campus. (Obviously this didn't happen last semester, since there was no NB class, but let's say that it's generally true.) That would be a total of 240 apps, and if they extended the deadline to get more applicants who had finished their pre-reqs, it could definitely get up to about 300. Because it's a pretty small number (in the grand scheme of schools and applicants), it could easily fluctuate from year to year and semester to semester, as well.
It may also be that the fall semester is a more popular time to start than the spring semester.
I assume they did this instead of the de-facto rolling admissions in order to choose the most qualified from the whole group at once. I don't know that it's going to work out the way they want, since so many other schools have already required deposits and orientation, etc.