For much the same reason folks choose fiberglass or laminated bows over self bows……personal preference. Personally, I shoot them because I’m on the poor-house end of the financial spectrum, and with care, a dozen carbon shafts will last me a number of years (I only target shoot with one arrow). I get “wood grained” carbon fletched with turkey feathers so I can pretend they are wood.:D Carbons are consistent and very tough….I’ve killed multiple critters, rocks, and stumps with the same arrow over several years.:D
With that said, I do think about going to wood one day. The smell of cedar and the romance of wood is hard to ignore. That will be another step forward, to begin tapering shafts, etc. I will add….I make switch cane arrows from time to time, and I have to say they are very near carbon in terms of strength.