Because; The normal procedure was that you open an account, the normal background checks are done, and then one goes to a gunshop/dealer and picks up his/her rifle. In this case mm talked the bank into going along with his making it look like he opened his account and the bank hamded him the rifle then and there. Thus making it look very slipshod and insecure.
I don't think he was going to show the whole 10 minutes waiting taking up his movie time. He does make available the outtakes showing the rest of the procedure. Yet people out there claim the whole thing was staged, when it was definitely real. Kooks like that do a disservice to those pointing out the real lies in the movie.
I can't believe I'm defending this POS movie, but that scene isn't enough to get me riled up.