I think it's one of those things you notice once you're looking for them. I certainly see them fairly regularly, in my smallish MidWestern city.

As a random example, yesterday I bought fast-food fried chicken for lunch. The woman who took my order was wearing an Apple Watch. The barista at my regular coffee shop wears one.

They're definitely showing up on non-tech people. I've also never seen a woman wearing a smartwatch that isn't an Apple Watch.