Free Online Dating Sites, ads supported only like OasisActive, AmorenLinea, DatingChile or DatingArgentina, had failed even in the South American Market, where nobody has credits cards or nobody wants to pay for a membership.
Only ads supported sites failed because operating costs are bigger than revenue; and other previously free sites had morphed to freemium ones like OkCupid and PlentyOfFish; they both had paid options with their free proposals. They encourage you to upgrade your membership, to acquire their paid features like credits to send virtual gifts or to increase your visibility or to know if someone had read the message you had sent to.
Freemium sites also includes social dating sites like Badoo, Mamboo, Yangutu and others like them with several lines of revenue like ads, micropayments, selling data from their databases to third parties.
Freemium Online Dating Sites are only for fun, for entertainment purposes, for instant gratification, not for serious dating.
Purely paid sites will be only for serious dating. If a person does not pay his/her membership, it is because he/she does not want to be serious dating online.