Earlier quoted context omitted.
I think it’s cultural. American society absolutely looks down on those that live with their parents as failures. If I were to guess, some parents might see their children asking to return home as a reflection on their ability as a parent to prepare for the “real world”, but that’s just my guess.
Only a certain vocal rich segment of American society.
In the US context, it has historical connections to the glorification of pioneerism and expansion through the western frontier (along with the genocide that accompanied that).
After that, in the post WW2 period, opportunity in the US was so abundant that a (commonly white male) school dropout could walk into a factory and get a job with benefits. The same person could then afford a modest house (not the gigantic houses of today), support a family on a single income, and had access to affordable health care and good public education for their kids.
In the context of that sort of opportunity, staying at your parents' home in adulthood was far more indicative of personal failings, and that's where the current trope disparaging adult (mostly male) children living at home originated.
But given how diminished all of those opportunities are today (no lands to forcibly take from less technologically advantaged peoples, no new factories, expensive housing where jobs are available, high qualifications required), it's a trope that's pretty irrelevant today.