Not to be mean, but I use to be one of those menial workers (I've worked as a janitor, factor assembly, plastics, etc) and most folks were very much motivated but they weren't able to take aim at careers when they have children or relatives to care for. Also, not everything one may do for work includes what they truly aspire to do. Just because the work seems menial to you doesn't mean it's not a challenge for them. There's plenty of explanations but none of them fit with the narrative of listless proles.