Since we've been discussing hats in the comments, I'll throw out a few thoughts.
I think it was a fashion accessory as much as anything. Grab a purse, clap a hat on your head. As Roxie pointed out, it also gave women a way to deal with hair they only washed every week or so. But even after women bobbed their hair in the twenties and started washing it more, they wore hats. I think it was all about looking good. We ditched hats at about the same time we ditched bras, in the sixties/seventies. I think that movement was all about dumping unneeded clothing; we ditched gloves then, too. I think it's possible we got carried away and ditched some clothing that, while not necessary, was really pretty and nice and flattering.
Remember how I do antique-style ribbon floral stuff? Over at Vintage Textile, they've got a hat from the 1910s (same era as yesterday's post) that is an amazing example of what a creative person can do with some organza, ribbon, pipe cleaners, wire, and a needle and thread. I saved all the available photos of it, for inspiration.
Maybe I'll start wearing a hat...