Hi, English isn’t my mother tongue so I was asking myself that question since I first encounted a w/… Back then I was like: “What tf does ‘w slash’ stand for?” And when I found out I was like “How, why, and is it any intuitive?” But I never dared to ask that until now
Tbf iirc the USPS had to make sure they didn’t conflict with other previously existing abbreviations. Although as someone living in LA, CA* they didn’t quite succeed
(Not Louisiana, Canada but the other one)