I'm not sure about DDB, but I know in AWS in general building a new service does not give you credit by default. It's not like the shit Uber promoted: Yeh! We have 8000 services. Look how great we are! In fact, people usually question if someone proposes to create a new service. Working Backwards (i.e., solving real user problems) and Invent and Simplify are indeed two powerful leadership principles. And of course, the sheer amount of work involved in setting up a new service is so much that people have to think twice between starting a new service.

DynamoDB was already large scale at that time.

The point is: the number of services don't need to scale with the level of demand.

My comment was about " paper fails to acknowledge a FOSS database (once?) underneath it: MySQL/InnoDB (and references it as B-Tree instead)." should have been more clear