I did say "*at* Oracle* -- which is not the same thing as "*by* Oracle".
The Linux kernel is GPL2; ZFS is CDDL. That is widely-held to be "a serious licensing issue".
https://www.theregister.com/2020/01/13/zfs_linux/ ← by the author of Linux
"Don't use ZFS. It's that simple."
Oracle cannot change the license of the kernel. It could change the license of ZFS, but it doesn't want to.
Oracle could change neither and include ZFS, but if it did so, it would officially legitimise Canonical's view.
We can only presume that Oracle does not want to do that.
Me personally, I would like to see Oracle merge Solaris and Oracle Linux. There is very little R&D going into Solaris now; most of the dev team were let go.
A current Solaris kernel, complete with ZFS, with a current Linux userland on top sounds great to me. Perhaps SMF could be ported as well, to eliminate the ever-controversial systemd.
This seems to me to offer Oracle a way to compete, but I don't think it has any interest in that. As per Bryan Cantrill's excellent talk on Youtube, I think it's all about the money and nothing else.