People who are regularly out doors, as they go about their daily business, still tend to wear hats.
What has gone away is the hat as an affectation among people who work indoors. If you are out in the sun all day, or out in the sprinkling rain all day, you wear a hat and it becomes part of your normal attire.
The exception is the construction worker, since he is obliged to wear a hard-hat and no one wears a hard hat once he’s off the job. But even a lot of them will have another hat to wear once the hardhat goes off.
The hat as a fashion statement died among office workers because it was just a fashion accessory and had lost its practical purpose.
I think that's right. I had been hatless all my life until I started walking my daughters home from school. This is in DC, with subtropical summers. Within a year, I was wearing hats. I also went seasonal on suits, although I never got all the way back to summer whites.
I think what killed the hat was mass suburbanization, which put most people into their cars for commutes. If your exposure to the outdoors is limited to the walk in from the parking lot, hats are an unnecessary encumbrance. People who still spend quality time outside still wear them.