as for what you can do for your friends, there's probably not much. the best you can do is to live well yourself and be a good example for them. also, be careful. there is some truth to the saying, "you become the average of your five best friends." if you get too involved in their day-to-day, you will experience friction when it comes to accomplishing your own goals.
I'm betting on housing cost and low quality of life for youngs, but well, I do have very little evidence to substantiate it.
the common thread I see is that living with their parents simply offers a higher standard of living than they could have if they moved out. I live in a relatively low COL area, so they would certainly be able to make ends meet if they cut the cord. but they would eat worse food, have a smaller room, and little money left over to save or go out. I imagine it's hard to find to motivation to work harder just to move out and decrease one's standard of living. I was very fortunate to land a good job straight out of college where I was actually able to increase my standard of living after moving out (although I do miss my mom's cooking).
I'd argue that this isn't inherently bad, but ultimately this can amount to "eating one's seed corn". In the long run, twenty-somethings that do this risk a financially more perilous life and a lower chance of being able to give their kids a good start in life.