not for "no" reason, but if they run off it'll be some reason you haven't noticed - can be too wet, too dry, too hot, too cold, too bright, or not enough bacteria to eat, like in a bin set up at the same time they're introduced

vermicomposting has 2 purposes: to get rid of your kitchen waste when you don't have an outdoor compost pile, or to raise worms .... if you have a useable compost pile, they require less attention than worms, but if you think you're going to just "harvest" the natural duff from the property, I'd say that has a better purpose where it is, vermicompost for your compost

Bill

I've noticed a few worms almost always crawl out when I first set up a new bin. But after that, they eventually settle down and decide they like it in the bin after all. And I'm not too concerned about earthworms indoors. They don't do any damage and they just squirm into a corner to shrivel up and die. :'( Poor things! If I can catch them quickly I can throw them back into the bin before they die, but I'm not always so quick to find them. I'm not grossed out though so it doesn't bother me. For more squeamish people it might be a bit of a shock to see an earthworm squirming across their carpet, though! I once had a dream where I got up in the morning and there were thousands of earthworms all over the place--in my carpet, squirming up my walls and dropping from my ceiling! It was like a scene from an Indiana Jones movie! But of course nothing remotely like that has ever happened in real life. The most worms I ever found outside of the bin were 4 once.