There was, is, and always be good applications for straight wieghts.
Marine is still on that list.
I live in michigan, and used sae30/40 in the boat.
My bayliner I ran over a decade before I purchased, then I owned five years.
1980 Islander 28' gm350. It seen pcmo 5/10w-30 or hd30 till I started service, well over 15 years.
First 5 years was hdeo 15w-40, ussually pennzoil.
Last 10 years before I sold it it got straight 30/40 hdeo only. Ussually HD40, heck it left with virgin pail of mystic HD40. So four more seasons for that beast.
harvey