It's all the TV programmes promoting housing as investments and not homes. The buy to let mortgages and all the wannabe landlords with their "portfolios". Snap all the flats and new builds up off plan to rent out, don't let a young couple get a chance - but they can rent it for more than their mortgage would have been no problemo.
The same reason why concert tickets sell out within minutes, or sales items are snapped up down the shops. Not for personal use, but to sell on for a profit.