You're right, and they also have jails and the FreeBSD service command seems to have been the inspiration for systemd (or is at least so close that it could have been). I think people are just unaware and afraid of trying "new" things.
- solaris and freebsd share very little as codebases and are very different OSes
- and regarding the previous point: the fact that some OSes shared the codebase ~30 years ago means very little today.
- the zfs people use on FreeBSD today is basically ZfsOnLinux. Som years ago the freebsd people dropped their snowflake implementation and joined the ZfsOnLinux effort, basically because ZfsOnLinux was moving at a way faster pace than they were. The project has been renamed OpenZFS iirc, and FreeBSD periodically rebases on that afaik.
I thought zfs came from Solaris/FreeBSD