How do survey sites pay for cryptocurrencies?

Excuse me, could you please clarify how survey sites manage to pay out in cryptocurrencies? I'm intrigued by the concept and would love to know the mechanics behind it. Do they hold a cryptocurrency reserve or do they convert traditional currencies into digital ones upon completion of surveys? Are there any specific cryptocurrencies that are more commonly used for this purpose, or is it a versatile system that accommodates various digital assets? I'm eager to learn more about this fascinating aspect of earning through surveys.