The reason why ZFS didn't plan out were simply because it was using too much CPU and Memory.
I am not sure that is the reason. Apple did already announce it at WWDC after all. ZFS on OS X was announced in June 2007. In September 2007, NetApp sued Sun over patents violations in ZFS.
It's likely that Apple didn't want a patent suit after adopting ZFS as their main file system. 2007 Apple was of a completely different size as 2014 Apple.
They announced support for it, not that it was the new default. Big difference.
ZFS support made sense for Mac OS X Server back in 2007. It's a beefy server filesystem that rewards beefy servers with gobs of ECC RAM, RAID, and no battery to worry about.
ZFS as default replacement for all of Apple's HFS+ usecases (laptops, iPods, phones and tablets in the works) made no sense in 2007 and makes no sense in 2014. ZFS is simply too resource intensive and too dependent on ECC RAM even now for consumer use cases.
I am not sure that is the reason. Apple did already announce it at WWDC after all. ZFS on OS X was announced in June 2007. In September 2007, NetApp sued Sun over patents violations in ZFS.
It's likely that Apple didn't want a patent suit after adopting ZFS as their main file system. 2007 Apple was of a completely different size as 2014 Apple.