AWS has few services that I imagine yield massive margins with not that much cost to them, which can mainly be justified by the services being pay-per-use and having a small overhead for the customers. And then, I believe most of the AWS's profits come from its enterprise customers which they have plenty of (who aren't in turn that price-sensitive as long as they see profits from their end).

DO on the other hand from my experience has been catered towards small businesses or hobbyists who simply just don't bring that much money vs even a one giant company will bring. And since DO doesn't have all the goodies of AWS, it can't really directly compete with it for those big customers.