Mostly that Postgres is amazing, runs anywhere and supports jsonb (which I use a lot). And I don't want to worry too much about mis-modeling; that's the entire point of a relational database with a type system.

Plus all the Mongo horror stories from people who I know and hold in high esteem. And recently talking to a data person explaining what a pita getting data out of their Mongo monstrosity into a format adequate for analysis.