The Atlantic scoops up the hypotheses:
When I asked Sheila Williams Ridge, who teaches early-childhood education at the University of Minnesota’s Institute of Child Development, for any insights she could give me on why kids love garbage trucks so much, she thought of her own daughter, now 21. When her daughter was little, Williams Ridge remembered, the weekly arrival of the garbage truck was both dazzling and, in a way, reassuring.
“Humans have always thrived with routine,” she told me. “But children, their memories aren’t long enough. Sometimes, when we’re getting our 3-year-olds dressed for winter, they’re like, ‘I can’t do it!’ And we’re like, ‘You’ve put on snow pants before. You’ve put on boots.’ But for them, it’s so long ago. They don’t remember snow from when they’re 2; it’s new again for them.” So having something happen every week at the same time—and especially something that “seems a little bit magical”—can boost kids’ sense of familiarity with the world, not to mention give them something to look forward to.
Plus, what the truck is actually doing when it arrives has an air of the forbidden. Despite the fact that kids are frequently discouraged from making messes at home or at school (or perhaps because of that fact), “children love dumping things. They just do,” Williams Ridge said. “So the fact that a truck is coming to do this on purpose, and everyone is happy about it? It’s like, ‘Yes! This is my dream! I just want to dump stuff out, and you let this person do it!’”
I loved watching the garbage truck when I was about 4. I still have no idea why. Any parents want to hazard a guess?