Lack of building can play a part but even the interests that want housing as investment naturally want to limit supply. The main thing is that the US has been

Lack of building can play a part but even the interests that want housing as investment naturally want to limit supply. The main thing is that the US has been printing dollars for several decades - primarily to deal with or prevent periodic financial crises. Ben Bernacke's "Helicopter Dollars" speech was infamous but nothing has changed but the (increasing) scale (and, yes, all the central banks of the developed world are doing it too). Effectively, the modern order has come to involve an endless hand-out to those who already have money while "market discipline" prevails against those who don't. Of course, this has long term problems aside from its immorality.