Live in the area you mention and everyone in my riding groups wears glasses or goggles. I tend to see more people wearing glasses or goggles than not. I often see people not wearing them for the climb, but they come out for the descent. But you're right... there does seem to be a growing crowd of non-wearers... which is crazy... it's so easy to take a stray branch or rock or mud to the eye. And that's while riding... even easier to seriously injure your eyes while crashing into the woods. I consider them as essential as kneepads.
I think people don't want to shell out for a quality pair of glasses that work well in all conditions... and perhaps they just don't know what's possible from a great pair of glasses. I switch back and forth between goggles and glasses depending on riding conditions and weather. For glasses I use the Ryders Eyewear Fyre lens (the "Roam" specifically). It's insane how well these lenses work... the anti-fog is the best I've ever used/seen/heard of. They have a huge photochromic range that works crazy fast. They're so good I put them on at the beginning of my ride and totally forget I'm wearing them (climbing, descending.. all of it).
I think people get tired of shitty glasses that fog up or are too dark in the forest and then not dark enough in the sun, etc, etc, and just stop wearing them. If more people invested in proper glasses... more people would be wearing them.
I also think it's sort of becoming another douchey "cool guy" trend... Day 1: "Ya, I'm so awesome I don't even need glasses". Day 2: "Ya, sorry, I can't ride today... scratched my cornea...".