I think when you're really good at using a computer, you expect things to be easy. When you get a sign up form instead, it's extremely frustrating. We're used to it being easy to use a computer and can see that someone is making it hard for their own benefit. And then we think, if it's hard for us, it's even harder for someone without a lot of skills.
And I think that's probably true! But the person without much computer skills comes in with an expectation that stuff is gonna be hard. The egregious signup page isn't a surprise in that sense, it's just one of the many things they have to struggle with to use a computer.
An A/B then doesn't show any benefit for removing the signup page, only downside, because an A/B test only tests what happens if one feature changes. Our intuition can still be right; if we could do all the work to make it so a website is actually easy to use for someone without a lot of skills, like how Apple radically simplified the state of affairs with the iPod, that will positively defy peoples' expectations and make the app more accessible -- even if just simplifying any individual component doesn't do that.