It's only in the last couple generations we've decided young people should be out of their parent's place by the time they turn 18. It used to be they lived there for many years to build up the necessary nest-egg needed to go out and find somewhere of their own. Even now I know a number of people who did it; it allowed my wife to save up and pay for law school completely on her own; and her parents had the extra space, no point in it going to waste. And as SJHovey mentioned, multiple generations living together comes with a number of advantages (grandparents babysit the children, children and parents provide physical help for grandparents, parents make the money knowing they have people at home) that can be had if it is done correctly. Frankly it's less of a waste of resources, too.
Now, if young people everywhere have to do it because a generation is so helplessly poor, then yes, that is an issue. But that will show up in so many more meaningful statistics than "oh no some people in their 20s are living with their parents" clickbait for easily-led-astray halfwits.