There are of course many factors, but the largest driver of cost increases in recent years have been materials and contractor profits. There aren't enough contractors and they can name their price. Unfortunately labor isn't really part of the cost driver, and basic laborers like carpenters are still under-paid compared to the wages that would attract people to the trade. Basically the American economy is now rigged to direct all earnings to middlemen and "thought workers" so nobody wants to just swing a hammer.

I often think about it like this - what job would you prefer for your child - work on building a road, or be a lawyer arguing whether or not that road should get built?