Because you set all partitions to F2FS. Only need to change /data to F2FS. Leave system and cache ext4. You would need a ROM with a patched fstab and then a kernel supporting f2fs for system and cache to be in F2FS as well. Plus major benefit is in /data, not system and cache. I tested full F2FS on my N4 and it was more a pain with less gain. /data is all that should be F2FS.
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