My impression (based on their Readne) is that the author did this not necessarily for readability, but to remove the abstraction that the database engine provid

My impression (based on their Readne) is that the author did this not necessarily for readability, but to remove the abstraction that the database engine provides in the form of the query planner. The developer is then responsible for selecting the index and storing their data appropriately, which gives more predictable performance and makes reasoning about the behavior of the query simpler(for beginners, not necessarily easier). This is very much in the pattern of DynamoDB (which they cite), which gives highly predictable performance at all scales by removing the query planner layer and leaving the developer to work out what indexes they need, how to mold their data to them, and how too query them.