True until it can be "monopolized". I guess in the near future govt will regulate green energy to some model that can give enough profit margin for corporates, and that will increase green energyp price to near fossil fuel, with bigger margin. Subscription based solar panel and electric vehicles come to mind.

As for reddit and twitter it's not the efficiency and room for profit, it's the cost to provide said content outweigh the revenue gained from ads. Hosting and maintaining global social media is expensive, which is there's no many players in that field.