Because NoSQL is a hype.<p>Many of the NoSQL essentially takes us back to 60s before Codd came up with relational model[1] These ideas tend to come back once in a while [2][3], but so far nothing is better than relational model.<p>NoSQL still makes sense in many cases (generally when your specific use case does not need all guarantees of ACID), you can get in return higher performance or horizontal scalability.<p>MongoDB is aim to be generic database but rides on the wave of NoSQL &quot;coolness&quot;. It was created by people who had no experience in databases and are learning as they go[4]. As they started adding things that are essential for database they realized it&#x27;s not that simple.<p>Currently MongoDB is outperformed by Postgres. In fact there is an application called ToroDB which provides protcol compatibility for Postgres that emulates MongoDB and even that outperforms Mongo. Mongo also doesn&#x27;t scale well horizontally, so essentially you don&#x27;t really don&#x27;t get any significant advantage.<p>[1] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Hierarchical_database_model" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Hierarchical_database_model</a><p>[2] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Object_database" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Object_database</a><p>[3] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;XML_database" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;XML_database</a><p>[4] For example they started with mmap&#x27;ed memory regions to store the data. Did not initially use fsync() to make sure data is saved on disk. In a way it reminds me of MySQL several years ago. It&#x27;s much better now than it was in the past, but it has a lot of warts left of from the past.