If Linux had been under the CDDL, ZFS would have chosen another license. Sun management at the time saw Linux as their primary competitor, and ZFS and DTrace was the crown jewels of Solaris. Just open sourcing was reported to have been a long internal struggle by the people involved, and there's no chance they would have let the Linux distributors use them for free.

Good or bad, it's the result of another era. Still impressive stuff. It's only recently that things like btrfs and eBPF became usable enough, and not in all situations.