Where Have All the Earthworms Gone?

I’ve been living in Seattle since 2012, and as far as I can remember, I always used to see earthworms whenever it rained and the ground was wet. They would be all over the sidewalks, and I’d have to watch my step to avoid stepping on them. Now that I think about it, I feel like I haven’t seen any in the last 3–4 years. Has anyone else noticed this? What happened to the earthworms?