At the time ZFS on FreeBSD came with some pretty serious caveats regarding performance and memory usage. It was pretty clearly designed for servers and not real

At the time ZFS on FreeBSD came with some pretty serious caveats regarding performance and memory usage. It was pretty clearly designed for servers and not really the sort of thing designed to run on your laptop, much less iPhone. Apple probably made the right choice for technical reasons alone. Since then ZFS has improved and machines have become faster.