Home prices have gone thru the roof. Avg home size also growing?

Saw the following chart (bottom) which shows buyers are paying more for less. What the chart doesn't show is the context. From 1973 till 2015 where this chart begins the size of the average home more than doubled.

What's the cause of the home price rise? 1. The 2008 recession caused legions of construction related workers to exit the industry. Ergo a shortage of labor. 2. Zoning in many places creates land shortages. 3. Interest rates after years of quantitative easing normalized. Texas and other border states will end up producing a ton of new homes as they now have lots of immigrants to learn the construction industry and more permissive zoning law (& available land).