

I’m going to guess it’s because of some linux native things. I remember source engine games used to have issues with non-ext4 filesystems (or maybe it was just workshop stuff as I still have left 4 dead 2 on a separate disk), but I’m pretty sure that’s been fixed.
Been running BTRFS and XFS partitions for years, so it’s certainly a rare issue.

Note: BTRFS defrag will result in a different copy at the end of the day. If you’re using snapshots this will lead to increased utilization.