You're asking why visitors are NOT signing up? Simple: ask yourself why they SHOULD sign-up. That's what your visitors are asking themselves when they see the Sign-Up button: "why would I sign-up?" And if at the moment they're not signing-up, it's either because a) you're not presenting the benefits of your site in a compelling enough way or b) people just don't see the benefits of signing-up for your site.
May be you could go to a Starbucks and ask 10 random people for some feedback: "Hi I'm an entrepreneur and I built a website. I was wondering if you could give me your opinion." Everybody loves giving their opinion. Ask people what they think would be the benefit of using your site: until random people can answer that question, you need to keep iterating. As a counter-example, if you asked 10 people what is the benefit of using Google, I'd say most would answer "Well, you find what you're looking for." Part of your job as an internet entrepreneur is to build a site that gets this kind of clear and easy answer. And when you reach that stage, then the next step is to make as many people as possible visit your site. But not the other way around!