Although it has been a couple decades since I've worked on construction sites, the underlying factor is that of the culture - this was northern Alberta - you had to be 'tough' and that meant eating steak, drinking hard and ignoring basic safety protocols like dust protection masks, eye guards, etc.

I was in my early 20's and worked with guys only a few years older than me that were already bordering on obese. The physical nature was typically repetitive and while sometimes requiring raw strength, had very little cardio/endurance aspects.

Of course there were exceptions, like the wiry 'old guy' who could take two bundles of shingles up a ladder over his shoulder and slam three beers for lunch.

They were being paid crazy amounts (for their age and the rest of their peers) and it was spent on rye and weed.