The PC versions of Beat Saber have the ability to play custom maps builtin out of the box. The Quest version does not. Oculus has promised to bring the ability to Quest but has not done it. Many thousands of Quest owners use BMBF and If Oculus all of a sudden cancelled the Facebook accounts of everyone that is using BMBF, they would have a PR nightmare on their hands, especially since they haven't followed through on their promise.
The worst I could see would be them giving people a warning that after a certain date they have to remove it.
The downside of BMBF is that is disables multiplayer, including comparing top scores with friends.