I work for one of the large MOOC providers. We "sell" "certificates" as a means to enable us to keep on providing education for free for those who would otherwise not have access to it. Certificate sales enable us to function (e.g. pay for staff and infrastructure) and work with our university partners in putting on courses for free.

Every day we get email from learners complaining that we charge for certification. Everyday we also get email from learners thanking us for providing free education. It's a tough balance.