Modifying data in /var/lib/docker/volumes

Hey all. I’m using Docker CE on Linux. I have a use case that involves modifying files in volume mountpoints from the host. I can’t perform the work inside the container. I noticed that the Docker docs say:
“Non-Docker processes should not modify this part of the filesystem. Volumes are the best way to persist data in Docker.”
However, no reason is given. I can’t see any reason why it would be a problem since it’s just a mounted filesystem. I fully expect these volumes to exist at any given time. If this is a problem, then I need help understanding the implications.