No, it's b/c of the document-oriented db system. All the field names are in every single one of the entries. Ex: If in every instance of 'Title' you had 't' instead. and every 'Post' you had 'p' instead --- it can add up to alot.
It is a property of document dbs, though I'm pretty sure implementations could internalize field names. Imma guess 99% of all Mongo collections ever created are pretty damn structured. When creating a collection, you could specify {internalize: false} or something to disable this when you do lean heavily on the schemaless behavior, but otherwise I'd like to see MongoDB take care of this.
