What would change if the rules became Official? Those who get banned for the most common reasons such as copy-pasting and spamming don't care about the rules anyway.
Some of them care... If they didn't care, would you see them opening up appeal threads on meta?
And those who do care and abide by the rules aren't affected by the name. Many rules are subjective by nature. What one mod considers off-topic might not be completely off-topic by another mod.
The name changes the perspective of how some members view the rules. You may view them differently now because you are an older member and you know what to do but If one is a newbie, things maybe different.
It happened to me that's why i made a suggestion about it. At first when I saw "Unofficial List", I Ignored reading them but had I seen "Official forum rules" or "List of Forum rules" it would have been different
Moderators' decisions varying surely can't stop them from being official rules of the forum. They are supposed to be like a standard or benchmark against which decisions will be made. Of course not everyone will follow them, but they will help to guide the members who are willing to be within the limits.
Your Country for example has Laws but has their existence stopped any crimes at all?