I personally see why MongoDB switches its license and clarify their original intention of using AGPL.
I even didn't know it was AGPL until now (I'm not MongoDB user). Because so many people seem to use it as if it is Apache License or something free of charge. I haven't see any warnings on AGPL and its implications in MongoDB tutorials on the internet.
The drivers are all permissive OSS licenses. It's on purpose, they never wanted to own applications that are built on top of MongoDB, but they never wanted to give away the server bit either.
I meant people seem to install the server too, thinking that the server itself it free. Most of MongoDB tutorials on the internet starts with "how to install locally" without mentioning nothing about the license.
The server _is_ free. As long as you don't modify the server, you don't have any obligations. If you do modify the server, you're only obligated to publish the changes you made to the server. No one is at risk of violating the license by installing it locally and using it in an application.
I even didn't know it was AGPL until now (I'm not MongoDB user). Because so many people seem to use it as if it is Apache License or something free of charge. I haven't see any warnings on AGPL and its implications in MongoDB tutorials on the internet.