Your question is "Why" but the answer posted is "How".
I don't know "Who" down-voted you which is the only definitive way of finding out "why" because we can ask him or her.
I suspect the reason is they felt you were looking for someone to debug your script for you and/or they had little appreciation of ruby. Personally I skip over questions where I know nothing about them.
As for your question itself you might want to consider something other than pactl because I've had problems with it setting the volume accurately myself. If you read this: Terminal command to set audio volume? there are other options available.
Consolation prize: I'm up-voting your question here in meta :)
