Its just that Solaris and FreeBSD systems were primary servers. If ZFS is the best file system, why not just use it?
I would really like to use native encrypted ZFS and then to encrypted backups with 'zfs send'. I would like good check sums, snapshots and all the features of ZFS.
Its simply overall the best system, I don't think there is really series competition. And the FS is one of the single most important parts of a OS. ZFS could be a major reason why people move to PopOS.