Why is thicker wood so expensive

Many people ask why its so hard to find very thick wood such as 3 or 4 inch thick. When kiln drying, every time the thickness is doubled, the defect rate, or the number or things that happen to the wood to make it undesirable, squares. In addition, the amount of time it takes to dry the wood also doubles. So 2 inch thick wood will have 4 times the drying defects, and 3 inch wood will have 9 times the drying defects. There is a tool to produce the thicker wood, it is called a vacuum kiln, and they start at about $100,000, a little out of reach for us. It is possible to air dry thick stock, but it also takes a very long time, the last load I did took 18 months.