Hype and lack of critical thinking abolutely had their role, but mostly because it's so much easier than a relational db.

Relational db's are hard. You have schemas and query planners and the truth is, you have to take care of every single query. Every query counts.

The same query can take 30 seconds, or 30 milliseconds to run, depending on it using an index or not. You think it's ok for it to take 2 or 3 seconds, until it hits production and halts the server.

Mongo doesn't have any of that. Just load and dump json back and forth, which is perfect for fast prototyping.

Who cares about data integrity or technical debt?