The ZFS installer was removed from later non-LTS releases. AFAIK, even in the version with the ZFS installer, it wasn’t in the kernel, it was just including the pre-compiled non-DKMS driver module that matched the kernel version.
That’s inaccurate. I’m was running that kernel when it came out, just the kernel no extra modules or anything get added except the libraries and commanda for ZFS and zpool. I’m on a more recent one these days and it’s still the same set up.
I can’t say I care about it being an option in the installer, I’d rather run an advanced install because the installer’s ZFS set up was garbage, everything in one zpool, no branching no data encryption etc etc.