DynamoDB is just not good. It has a document size limit, and throttling. It gets very expensive very quickly. And it's not fast. Writes are slow. And it's difficult to query.
Yes DynamoDB is indeed quite expensive - and increasingly so as data size and traffic grows. The whole point of distributed datastore like Dynomodb is to scale out massively by compromising on many database features and flexibility, but what's the point if it becomes so expensive at large scale?
