The ability to do so is enshrined in Item 6 of the Open Source Definition: https://opensource.org/osd-annotated
The Open Source Definition provides a single point of reference for what it means for a project to be "open source."
Licenses are submitted for approval by those who wish to prove that the license provides the benefits and freedoms assured by the Open Source Definition and therefore by open source.
Licenses that do not provide each benefit and freedom in that definition are not not approved and are not—literally by definition—open source.
MongoDB recognises the value that a consistent worldwide definition of open source provides to the entire software development ecosystem and is seeking approval for their license to show their support and respect for the definition.