It's because mongodb just isn't as good at queries as a relational db, while also not offering the scalability benefits that other nosql databases do. Also the

It's because mongodb just isn't as good at queries as a relational db, while also not offering the scalability benefits that other nosql databases do. Also the attitude that mongodb takes towards data - namely, convenience and performance first, data safety second - is very incompatible with most uses for a database.