Mongo’s “return before write” behavior is what earned it this title. It makes it look better on benchmarks, convincing unwitting devs that it is a better choice.
Mongo and NoSQL, to me, are really symptoms of the Bootcamp craze that happened a few years ago.
It's way easier to understand than relational databases, can be simply browsed and retrieved as json (usefull when your only language is JS) and had good adapters for the cookie cutter frameworks used at the time. And you don't need to bother with a schema or joins.
There are use-cases for NoSQL but it's not a once size fits all solution.