The issue is "physically demanding", look at the guys that are 50+ in the trades, they have all sorts of physical issues from working in the trades. I say this as someone who has two JM qualifications.
The confounding factor is lifestyle. Kicking back after a hard day of physical work with a huge meal and a few beers feels amazing, but that's going to wreck somebody's health if that turns into a lifestyle. And similarly, a gym rat who works a desk job is going to probably be in excellent shape.
*Edit : though/tough, not native
I know 5 people closely that have had long careers in the trades.
They are all physically damaged in ways I am not from sitting at a desk.
What I notice about the trades is that the conversation from the inside is mostly about retirement because the work is not fun the way I find my white collar work to be fun.
You also have to appreciate one other thing about health. 30-40 years ago digital work was a very small part of the labor force. Today it's a large part. So we're only starting to see the long-term consequences of sedentary work, on a large scale in relatively recent times. Then you also need to pair this with the emergence of endless entertainment of the internet to also create the possibility of sedentary work paired with sedentary lifestyles. I expect we'll find that the aggregate health outcomes of this are going to dwarf even smoking.
[1] - https://www.cdc.gov/nchs/data/nvsr/nvsr74/nvsr74-02.pdf