They're getting your pageviews, clicks, and just generally interaction. If you aren't blocking ads, and they've got a 100 question quiz, with each question on a new page, they can get hundreds of ad views out of you clicking through the quiz.

Basically they make money the same way Google does... they just attract you with a fake service instead of actually providing something useful like Google.

I even used one of those types of things that did actually pay out a long time ago. It was a knockoff search engine that 'paid' you a couple points to use it, along with doing quizzes and the like, and after earning several thousand points over several months, I successfully "cashed out" a $5 or $10 gift card.