It's only been available out of the box in a simple-to-use and supported fashion in 1 Distro for barely 1 year.
You can hardly say it's been widely available, nor for a "quite some time".
As for it not being widely available... you're saying the only way for something to be considered widely available is to be included in the distro directly? I'd argue an easy installation/setup and solid documentation are FAR more important than being included in a distro. If the setup is arcane or the documentation is horrible, it doesn't matter if a tool is in every distro on the planet, nobody is going to use it.
I think your "barely a year" metric is far off.
Ubuntu is the only distribution that official supports ZoL, and actually ships it in it's official repositories (and by default). What that means is that Canonical is effectively saying "we trust there's no legal reason why we cannot do this." No other distribution has made that claim.
EDIT: Actually NixOS also supports it, but the point stands.