Microsoft built this so they can have a MongoDB compatible database service for Azure.
A few years back MongoDB changed their license to AGPL to make it harder for companies to take their code and offer it as a service. They did this because it competes with the MongoDB Atlas service.
Mongo changed from AGPL, which is permissive enough to be usable by cloud providers, to SSPL which has even stronger copyleft making it unusable for cloud providers (and doesn't meet the OSI or FSF requirements).
A few years back MongoDB changed their license to AGPL to make it harder for companies to take their code and offer it as a service. They did this because it competes with the MongoDB Atlas service.