ORMs have existed for decades so developers can use a SQL database just fine without knowing the language. So it's definitely not this.
It's more likely because Mongo is (a) is extremely fast, (b) the easiest database to manage and (c) has a flexible schema which aligns better with dynamic languages which are more popular amongst younger developers.
Postgres is faster at json than mongo. Also the pipeline query strategy of mongo is terrible to deal with. A schema should not be flexible. Now I have to write a bunch of code to handle things that should have been enforced by the database. Postgres is incredibly easy to manage with actual default security. I know the mongo tutorial says to not run the default configuration, then why is it the default configuration. It's so easy to manage anyone can take it over for ransom.
ORMs have existed for decades so developers can use a SQL database just fine without knowing the language. So it's definitely not this.
It's more likely because Mongo is (a) is extremely fast, (b) the easiest database to manage and (c) has a flexible schema which aligns better with dynamic languages which are more popular amongst younger developers.