The second reason is because I'm a nerd and I wanted to be able to ironically say "remember remember the 5th of November..." :P
The first reason is that there's been a huge amount of reported content theft via a website called yiff party (DO NOT LOOK IT UP!) that offers up false pledges so that they can access the member-only content, only to then turn around and cancel their donations before they're processed.
Delaying member content releases pretty much prevents this and protects you all as much as it protects me. :)