As to supernatural causes, neither does the inexplicability of Pio's condition rule them out. As for the possibility of hoax, the Church itself was alive to this possibility. The first thing the Vatican did on getting wind of Pio's condition was to place him in a sort of internal exile that continued for nearly two years. In this period he was barred from hearing confessions, saying mass, administering the Eucharist — in short, barred from any exercise of his normal priestly duties.
Also in this period, the Church had him examined by doctors, scientists, "experts" for the sole purpose of falsifying Pio's claims. They couldn't do it, though they certainly could not falsify the existence of the physical wounds. Pio was a "scientific curiosity" for 50 years. He continued to be seen by members of the medical and scientific community over this period. If there had been a hoax involved, one would think it would have been discovered by now.