Sally says the last house to trick-or-treat looks totally abandoned, yet it's friendly-looking, lit well from the street and has signs of upkeep (no peeling paint or broken windows or leaf debris or trash).
This story would have viewers believe that a town with children disappearing every Halloween over a seventy-year-period would not have grieving citizens enraged with enough gumption to have the observance of Trick-or-Treating banished. At the very least, remaining kids would be severely chaperoned or sent trick-or-treating out of town rather than be allowed to go about on their own (especially unusual when you consider that this is a town where every kid scoots for home as soon as the automatic lights come on heralding the coming of night). Indeed, the emotional coldness of the Springville community seems represented in Sally and Watch, who are quite willing to immediately write off Marvin (just past the instance of his abduction) as just another unavoidable loss to the community, to be dismissed and forgotten about like a glass of spilled milk.
While all of the trapped trick-or-treaters have aged from the time they were snagged by Marvin, Marvin himself has not aged. (All of them do, however, mentally remain children.)
The story derives a happy ending while sidestepping the issue of Marvin having periodically eliminated children at whim.