Definitely a bit of everything. Mills shut down for Covid around this time last year, money from the banks got cheap at the same time people had lot of remodeling time on their hands. Demand shot through the roof and supply has really struggled to keep up. Tack on some devastating fires out west, tornadoes in the mid south and hurricanes in the deep south/east coast and it's really been devastating year for lots of people. Simply not enough material to go around, even at such extreme price increases.
I've posted about it before, but really would like to mention how impressed I am with Spooky in their R&M run. They presented a price in December of 2019 and stuck with it throughout the run, even with raw material skyrocketing (like, threefold in some situations) for the last year and change.