I'd say the main problem is that there isn't a fsck for ZFS. If important metadata gets damaged you'll have to re-create the whole file system.

W.r.t. to btrfs they are at least working on a fsck tool, even though it can't repair much yet (what it can repair is e.g. some bitflips caused by bad RAM: https://patchwork.kernel.org/patch/4116411/ ).

And stuff like ext4 or ntfs can get back to a state where one can write to it again in most cases.

Another problem is that many applications don't handle EIO well, i.e. they don't give you an option like "Continue with corrupt data", e.g. if a video file gets damaged it doesn't matter much, it'll just be a few damaged pixels, but the whole video player stops playback because it doesn't handle the IO error.