People are graduating into a recession and can't get jobs. They have massive student loan debts so they can't possibly save for a down payment. Millions have been chucked out of their homes, making it impossible for them to get another mortgage or even have decent enough credit to qualify for a rental. Of course there's a low rate of household formation.
I'm sure once everyone gets some confidence in... the confidence fairy... or whatever the hell, everything will get better.