Never went away, Linux is now the primary target platform for OpenZFS (which is basically synonymous with ZFS these days). TrueNAS/iXSystems (probably the main commercial company using ZFS) moved from FreeBSD to Linux. Major new features like pool expansion have been added after years of requests. Etc., it's a good time for ZFS on Linux.

There ARE licensing issues related to shipping it compiled into the kernel, but you can install it as a kernel module on every mainline distro nowadays which is functionally the same from a user perspective.

ZFS on Linux works great, but with most distributions, it will compile the kernel module on device upon installation. Only Ubuntu distributes binaries.

As a consequence, you don't necessarily want a rolling distro, as the ZFS module can get out of sync with the kernel.

ZFS itself is build for both BSD and Linux from the same source, so there's feature parity there.