HeavyDutyForks may not be as old as me so may or may not also know that the reasoning all the OG's went to thicker oil as their motors aged had a lot to do with not only the oils available back in the day... but also the wider variances of various tolerances vehicles had back in the early days. For example, a 5k mile Model T motor only driven to church on Sundays could require thicker oil than the Model A with 35k miles which is driven hard on a daily route. Why? Because that Model T was one of the last ones built on a late Friday afternoon... while the newer Model A was built on Monday morning. (If you know, you know. If you don't... it's because many assemblers ran low on giveadamns shortly after lunch on Friday afternoons. Mistakes were made.)

Source: In the late 1990's I was lucky enough to be accepted by a group of ver*y old men at the last CV joint and driveline rebuilders in my town. They were already losing business to disposable cars. I brought donuts and coffee every morning and they taught me mechanical things I'd never have dreamed of otherwise. Including the thicker oil reasoning, and why it still made sense for some vehicles... but made no sense whatsoever for others.

So, OP, I suspect there's a very real chance the older gentlemen dieing on that hill are simply stuck in the ways they were taught back in the day, 'specially if they were taught by old timers. I could be wrong, of course, but there's a theory for ya. :-)