I do live in Northeast.
However outside of my travels and cruises in Europe, NE/Canada and some others most of my almost 60 cruises were to Caribbeans, Bermuda, Bahamas. While I do see some shorts in MDR even on lines like Celebrity, people in shorts are minority in MDR.
I doubt it’s because “their wives make them” (I’m sure this happens too) or they are afraid of Maitre D or me 🙂 . All ships I’ve sailed on were very well air conditioned so it’s not like it’s too hot to reach restaurant (unlike it could be on land).