I know what you mean. When I first harvested my vermicompost - and before being educated on the wisdom of exercising moderation in using the vermicompost in my pot plants - I used pure castings to sow hot pepper seeds in a couple of pots. When the seedlings became yellowish and spindly, I moved them to my flower beds. The pots which were still about 1/3 full of vermicompost were left undisturbed for about two weeks. Then I decided to use the compost in a potting mix. When I tipped the pots onto the soil (I used granular burnt earth which I get for about 80 US cents per 5 kg packet) I saw three fat healthy worms at the bottom of the cast from one pot. A cocoon must have got left behind among the castings and the watering given to the seedlings sort of helped it to hatch. Later, even though the pots were left unwatered for two weeks, some moisture must have remained in the cast to enable the worms to survive. I do think that unless the odds are too overwhelmingly against them, the worms that hatch into a particular environment adjust to that environment.

I see this often and I am amazed at how they survive in almost a completely dry condition. I am famous for not harvesting my bins for very long periods of time and when there may be a new food source they don't all migrate there as the other areas are so full of microbes why use some muscle and move when its all around them so I think that your garbage bin is a microbe haven wet or nearly dry.