What is it about worms? Why are they suicidal?

After a rainstorm, or even during, there are earthworms all over the concrete. The cement seems to suck the moisture out of them and they die there and turn into worm-jerky. Why are they there?

I’m sweeping up carcasses from my patio now. There doesn’t seem to be any advantage to this behavior. Is worm jerky an important part of the pioneer bird’s food chain? My birds don’t seem to care… maybe because I feed them something else.