Where do they go? Are you kidding? Where do you think millennials are? Not only that, but when a baby boomer sells they will have well over a million dollars cash and not have to worry about job markets. Still infinitely better off than the younger generation. 

Why don't they move to condos? Millennials live in condos. It is fine. Except millennials are now at child-bearing age. Would you agree that a family of four needs a house more than a retired couple?