Homebrew believes MongoDB is no longer open source after modifying its open source protocol. The new MongoDB versions are not release under the open source license. So they are not accept by the Homebrew core.
MongoDB announced in October last year that it switched its open source license from GNU AGPLv3 to the Server Side Public License (SSPL). In response to cloud vendors such as AWS providing MongoDB as a service to users without giving back to the community. The SSPL explicitly requires cloud vendors hosting MongoDB instances. To either obtain a commercial license or open their service source code to the community.
However, the open source community seems to have a lot of objections to this. Many people think that SSPL is a soft target and seriously discriminatory to certain categories of users. This violates the true meaning of open source, so Fedora believes that SSPL is not a free software license. Cap and Debian also announced the removal of MongoDB from the distribution.

The Homebrew core list has now removed MongoDB and no longer supports it.
In fact, some people in the Homebrew community have different opinions on removing MongoDB, because MongoDB ranks 45th in the Homebrew core list, and has 25k installs per month. They think that removing it will cause inconvenience to many people.
But the idea of final removal is still dominant, and the change in open source protocols is the main reason. In addition, Homebrew also lists some reasons why MongoDB can be removed:
- Currently mongodb and mongodb@3.6 no longer build source code.
- It doesn’t make sense to keep an old version that is no longer maintain.
- MongoDB maintains a custom Homebrew tap on its own . (This reduces the damage done to the user)
See details:
https://github.com/Homebrew/homebrew-core/pull/43770
https://github.com/Homebrew/linuxbrew-core/issues/12582
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