You’d have to know the history of Home Assistant for it to make sense. Originally, HA was just installed on anything running Python.
Then components started being used, one of which was Z-Wave. So people would install HA, then install OpenZWave as a separate package on the same machine. The two had nothing to do with each other, other than both being able to talk ZWave.
All of a sudden, things started breaking and the developers were having to fix them. This was caused by people updating their Raspberry Pi/Linux to a later version, which updated components that HA used, which broke things.
This, the Virtual Environment was introduced. That’s where the Fabric script came in. It install the VE, installed HA in the VE, along with thing like OpenZWave, etc.
The problem is, that all of it was based on a particular version of Python. When Python support for that version was announced as end-of-life, HA re-wrote come of the code to work with later versions. Part of that is what “broke” the Fabric script.
Meanwhile, Hass.io had been introduced, along with Hassbian, along with the already existing manual installations. So now you have options on how you want to install.
The biggest reason for “killing off” the Fabric script installation was the fact that things like OpenZWave is no longer needed, unless you just want it. ZWave support was introduced natively in version 0.45 (I believe). So now there’s not really a “need” for the script. Plus, updating the script and running it under Raspbian Stretch still takes 2-3 times as long to install compared to the method I posted above. And using the method I posted above, you only install the parts that you want/need, so you don’t have your RPi loaded down running software that you won’t use.
Trust me, I’ve hacked the script and installed it on Raspbian Stretch more than once. At the end of the day, when I physically damaged my SD card, I ended up reloading it with Raspbian Stretch and using the method above to install. I was done in about 45 minutes, compared to the 1-2 hours for the script. And with the script, OpenZWave and MQTT still don’t install properly, so you have to manually uninstall them and reinstall them anyway.