>Because in just about every country adults are supposed to support themselves.

China, India, and Latin America make up an extremely large portion the world's entire population, and families from there have had a growing presence in the US. Multigenerational housing is the norm there, and is absolutely not a red herring. Additionally, the focus is on supporting the family unit, not supporting in one specific direction.

I definitely agree that high prices (housing in particular) are contributing to this, but so is culture.