I see 3 (positive) things those platforms provide:
  • trust. This is important when children want to take classes online. Maybe less so for adults. This can probably be achieved with a reputation mechanism.
  • promotion. They spend a lot of money on ads making sure teachers and the platform gain visibility with prospective students. In a decentralized platform, teachers could be given the tools by the platform to get their profile out there by paying the necessary fees.
  • conflict resolution. Mostly in terms of payment. In a decentralized platform, one could probably think of a escrow or multisig approach where the payment for the ongoing lesson only gets released after the class is finished, but without 3d party, it might be tricky... but we're talking 20$ amounts for a class or so, so with a good reputation system, this might not be unsurmountable.