A useful starting point in dealing with this (and the housing crisis in general) would be to determine what proportion of homes are not being used as a primary residence. I suspect it has risen dramatically over the past couple of decades. If it turns out that that is the case, the next step would be to find out why.
Another pertinent question would be the overall supply of housing: one obvious factor that could help explain the graph I just described is that the overall supply of US housing has gone down, meaning that fewer owners are in a position to rent out property at all. Hence the supply of rental properties is significantly decreased, which will drive up the price.
[1] https://www.statista.com/statistics/187576/housing-units-occ...