I don't think it is about it being wrong (though it is abnormal in the US context), it is the reason for this shift that is worrying.

Is there any reason to believe this is due to a cultural shift amongst Americans? I don't believe it is controversial that the young have been the most negatively impacted by rising education and housing costs, as well as their demographic being the most heavily impacted by the Covid-19 pandemic. (is it?)

The implication here is that more young adults are staying at home, not because they want to, but rather because they cannot afford to leave (or in some cases, as the article mentions, because it is better than being isolated at home alone). I hope you agree that this is an important distinction.