I agree partially. In the age of cheap backups and cloud storage, having super-high-integrity filesystems with easy RAID is more of a niche, so the need for ZFS on desktop and app servers is low. ZFS is fine as a general purpose filesystem, too.

In the end, I think it's momentum and licensing. AFAICT btrfs only exists because ZFS can't be shipped in Linux kernel. Defaults are insanely powerful, and ext4/xfs is good enough for a lot of use cases. If ZFS were BSD or GPL licensed, I think every Linux distro would ship with it as an option, if not a default.