That, plus sign-up is usually the top of a funnel to ask you for money later on.

So they want to have as many signup as possible, and they also want as many conversion from free users to pay users or whatever. The reasoning is that if they double the number of signup, they'll double everything down the line (forgetting that the "quality" of signups matters and making a user create a phony account just to access one page one time is useless).