MongoDB used to be AGPLv3. A year after their IPO they realized "aww shit, Wall Street wants continuous growth, being profitable isn't enough" and decided to migrate to a completely new license, SSPL, that's designed to put everything surrounding the software in scope of the copyleft. The implication being that if Amazon were to offer MongoDB they'd also have to release all of AWS RDS[0] as a thing you could just download and use.

The community did not like this one bit, but MongoDB doesn't need to care about what the community thinks because they had CLA'd all their contributors. That is, if you wanted something in MongoDB upstream, you had to give MongoDB full copyright ownership over the software. Which exempts them from copyleft[1]. One of the critical parts of copyleft is the "no further restrictions" rule; otherwise copyleft is just proprietary with extra steps.

[0] I don't remember if they were hosting MongoDB as part of RDS or something else.

[1] As we've seen with the Neo4J lawsuit, copyright licenses cannot tie the hands of the copyright owner. The only way for copyleft to work is to create a Mexican standoff of contributors who will sue each other to death if any one of them decides to relicense without unanimous community consensus.