When people wonder about how people are dressed in old photographs, I think a couple of factors are at play.
There were indeed different social expectations about how people would dress. It was not expected that men would wear suits all the time, but in white collar professions where dockers and polo would be acceptable today a full suit, or at least a sport coat and tie, would be required. Blue collar men wouldn't wear suits at work, but they would wear them on special occasions more often. They might also wear wool sportcoats and other things we would consider dressy to and from work, if not on the factory floor.
Today we might read more structured or layered garments as formal, but people back then didn't think of them as formal back then. For example, if you saw someone wearing a chambray shirt and wool pants today you might think, "collared shirt + non-jeans= formal," but someone in the 1930s would see someone wearing hard wearing workwear. Similarly, if you work outdoors, say as a shepherd or a farmer, in a relatively mild, but cool, and wet climate like the British Isles, tweed jackets and wool flat caps are extremely practical, but because it is a more tailored garment it seems more formal to modern perception.
Tailoring in the early 20th century had some features that made it more practical and comfortable to wear. (This is not comparing vintage bespoke to modern bespoke, but comparing what you could buy in Woolworths in 1937 to what you can buy at Kohl's or Macy's in 2017.) In particular, suit jacket armholes fit better. As a demonstration, put on a modern suit jacket, button it, then lift your arms into the shape of a T. Compare that to this pic of James Cagney. http://mydapperself.com/wp-content/uploads/2016/01/High-Armholes.jpg?3075fb
Modern mass-market, off the rack suits are often made from thin wool-polyester blends. Even high end modern suits use wools that are often much thinner and lightweight than vintage wools. (It used to be really hard to make so-called super 100s, which are common in suiting today.) Heavier weight wools (leaving aside summer wools, palm beach, linen and other speciality summer fabrics also often used in the early 20th century) translate to more practical suits because they can take a lot more abuse.
Some examples from photographs taken by the Farm Security Administration and the War Department: These berry farmers in Michigan aren't dressed formally at all, even to modern eyes. http://www.loc.gov/pictures/resource/fsa.8c36076/?co=fsa
These defense plant workers might look more formal to modern eyes, because of the wool slacks and collared shirts, but to someone in the 40s this is just everyday wear. http://www.loc.gov/pictures/resource/fsa.8c20135/?co=fsa
This is a picture of three factory workers being recognized for their contribution to the war effort, as you can see, they are all dolled up for the special occasion. http://www.loc.gov/pictures/resource/fsa.8b04884/?co=fsa
This Irish farmer is also wearing a suit, but it is much less formal, more hard wearing one. (Not all suits are the same: fabric, weave, and other factors can really change it into a workwear garment) https://i.pinimg.com/236x/f2/07/44/f20744c16c6d7de74f2f561386fe6c0a--irish-men-farming.jpg (not sure of the full provenance of this pic.)
Not sure about the West, but in Soviet Union back in 80s when you taking a plane you got to dress up. My mom insisted that I need to wear a white shirt, slacks and black shoes. Why ? I don't no.
