As you yourself mentioned, ZFS is different. The other projects were (for the most part) anonical originals" that they tried to create -- primarily on their ow

As you yourself mentioned, ZFS is different. The other projects were (for the most part) anonical originals" that they tried to create -- primarily on their own -- to replace existing products. ZFS is going on 15 years old, quite mature, highly trusted, and, of course, it already has a huge existing userbase. It's certainly not an internal Canonical project that requires them to devote huge teams of developers to it. Unlike the others you mentioned, ZFS will continue to exist and grow regardless of Canonical's involvement.