In countries outside of the US there is also trend of children leaving the nest later that before. This is especially notable in Italy and Japan for what I know.
Personally I correlate this mostly with pricing of housing that is essential and limited resource. Housing is hoarded by capital owners in purpose to lend it to people who have not amassed enough capital (yet).
Because of that price of housing raises uncontrollably to the point where almost no young people can afford not only buying a house but even renting one. In Japan when you start renting a flat you are obliged to give owner customary 'gift' that is worth two years of rent.
Because keeping house empty is small cost for owner it's better to keep it empty than sell it at lower price. This prevents prices from dropping even when there's no demand at high price. Prices of rent follow prices of houses.
Of course all of that is just my uneducated guess.
Personally I correlate this mostly with pricing of housing that is essential and limited resource. Housing is hoarded by capital owners in purpose to lend it to people who have not amassed enough capital (yet).
Because of that price of housing raises uncontrollably to the point where almost no young people can afford not only buying a house but even renting one. In Japan when you start renting a flat you are obliged to give owner customary 'gift' that is worth two years of rent.
Because keeping house empty is small cost for owner it's better to keep it empty than sell it at lower price. This prevents prices from dropping even when there's no demand at high price. Prices of rent follow prices of houses.
Of course all of that is just my uneducated guess.