Vacations...
Also, what's the point if the interview season isn't going to be any earlier? I suspect that most schools schedule the interview season to correspond to the return of M2 students from summer break (as they are often hosts and tour guides), the return of interviewers from summer vacation, and the completion of applications including MCAT scores, LORs and supplementals. If you think that some of the big feeder schools are going to be writing their letters 2 weeks sooner, you might be mistaken.
I have been a big believer in "be early or go home" but over these past 2 cycles I've seen that computerized files are making "being early" less advantageous. It is so easy to sort and skim the cream on a daily basis and leave the less desirable behind (although we set a 2 week deadline for looking at an application once it has been assigned to a reviewer). Consequently, a really strong applicant might get through the process and be invited for interview in 48 hours while a less desirable one might take 4 weeks -- and there is no telling how long you might sit just because there are 3,000 applications in the queue and not more than 600 are assigned to readers at a time.
Frankly, anything before July 15 is early. Secondaries submitted by August 1: early. Relax and enjoy the ride.