Why is it that my AIT is a year long but I can't smoke or dip?

Because the Army thinks that, even though you can be expected to have the judgment to learn to drive a $6.2 million tank, you don't have the judgment to determine whether or not you should smoke or dip. ;)

They want to see how you react when you're crazy.

Because the fact that you are a trainee apparently makes you irresponsible in the Army's eyes. You are expected to act like an adult & face adult consequences, but get treated like a child instead.