Years ago, when I worked on a photographic magazine, I interviewed the photographic archivist at the Museum of London, who had a fascinating take on documentary photography. He said that people traditionally took photographs on important occasions. So there are plenty of archived images of Queen Victorias Jubilee, VE Day, and local events such as weddings and parades. But what his collection lacked were shots of everyday life, when nothing special was happening.
He was actively recruiting photographers to shoot topics such as office life and London street scenes. Not the decisive moments that Cartier-Bresson sought, but the undecisive moments. He even specified that pictures should be taken from one end of a street, then half-way along, then the other end, and asked photographers to forget about all the photographic tricks... to make the pix as true to life as possible... to show people in future years what life in the late 20th century was really like.
I sell stock imagery, and one subject continues to sell: everyday people doing everyday things. Not models pretending (too stocky), but real people...