I blame the Anthropocene - specifically climate change, loss of habitat, and pesticides, though I'm sure all of the ill-fated and shoddily homemade terrariums I put them in as a child didn't help.
I also think part of it could just be the fact that most of us aren't outside, near the ground, digging through the grass and rooting around in bushes like we used to as children, which makes us way less likely to see or notice them as adults.