That’s because it is! Your steps would only work if the dependencies were already installed, like if the Zigbee binding were installed. If the dependencies are not met, then you need all of the steps listed in the readme to manually install it, which is a PITA… hence the script.
What version of script and where are the logs? My guess is that you supplied the wrong password the first time when you got an error about the serial transport. Rather than hijacking this topic, it would be better to troubleshoot this in your own topic or the script topic.
This sounds like an upgrade issue…