DynamoDB was designed to solve a very different problem than a traditional SQL database. When DynamoDB (and the other Cassandra flavors) were released there were no databases doing multi-master failover with high write throughput - we are talking about TBs, not GBs. It's not a coincidence that Google, Facebook, and Amazon all had to write to their own database at around the same time (BigTable, Cassandra, Dynamo).
With those new tools you had other companies building on top of those databases for far cheaper than a license to MSSQL or any other OLAP of choice would give you.