Life was harsh, lots of work was physically taxing (no machines to do the heavy lifting), and there was not much in terms of relief for any sort of chronic or recurring pain, like back pain, tooth aches etc. Alcohol helps endure, as it made you more numb to such pains. It might also help you sleep at night, when otherwise your aching body might have kept you awake.

In some physical jobs like the construction business, workers used to rely on alcohol to make through the work day until very recently. In some countries they might even still do so.

I can confirm from my own experience building a house and doing heavy lifting on the construction site, that after 10 hours of taxing work, an evening beer works wonders to relax your strained muscles and regain some feeling of comfort.

It's no surprise to me, that the reduction in alcohol consumption coincides with a switch from more hard physical labor, to more sitting jobs.