Mongo was AGPL until 2018. The AGPL didn’t stop Amazon from abusing the open source social contract, hence why Mongo modified the license.
It is what makes all the difference between MongoDB and Linux, for example. What happened to MongoDB could never happen to Linux.
AWS never offered a service based on the AGPLv3 version of the MongoDB server. Therefore the change of license terms to SSPLv1 was not directly caused by Amazon’s use of the software as part of an offered service, and had no impact to Amazon DocumentDB as an independently developed interoperable protocol implementation.
There were cloud providers headquartered in Asia that did offer AGPLv3 based MongoDB server as a service.