Maybe it is because we do not want many new users who are not bright enough to navigate the website.
the signup form should be accessible in one click from the front page. common sense.
For example, I go to my bank website and click "My Account" cause that's what I want to do. It asks me to sign in, and then redirects me to my account page. I don't click sign in.
I'm not saying this makes it ok. This just made me aware of my technique for the first time and I thought it was interesting.
How have you been, pot?