If you look at the process for making each I think aluminums are the ones that are too expensive. They can turn on a machine and fill a room with aluminums pretty quickly. But wood you have saw and split the bolts, then saw flitches, let them dry and season them, then run them through a molder/doweler, sand them, grade them, spine them, weigh them....after all this you have about 50% waste through this process that takes months.
Oh then the shaft manufacturers have to pay the excise tax on each shaft that is about $.40 (as I recall)!!! While the carbon and aluminum manufacturers have to pay this tax also it is a much smaller impact on their bottom line than for wood shaft manufacturers. Once again gov't making it easier to do business...NOT!