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.

you know those scams which say if you answer 10 questions you get 100 dollar delivaroo giftcards? their usually scam. how do the scammers make money

• The survey website could be filled with ads or other tracking bullshit which earns them advertising or sales revenue.
• The website could trick you into running malware, such as ransomware which pays money.
• The survey data could legitimately be used by marketing and product research companies who will pay money for that info.
• The survey could provide the scammers with enough personal info to break into your accounts, which could enable identity theft, taking out credit in your name, sucking your bank accounts dry etc. Or sell the data to other malicious parties who will do this.
• The cost to operate these survey sites is basically nothing, if the gift cards are even real they will be stolen or obtained fraudulently.

Gift cards can easily be converted to cash relatively easily and anonymously. You can do so without being in physical possession of the card--you generally just need to know the card's number.