Because Satoshi's identity and whether or not they were a singular individual or a group of individuals is unknown. It is entirely acceptable, and more often than not probabilistically and politically correct, to use they/them here.
I doubt anyone would be upset at people using he/him when referring to Satoshi, but also along those same lines, it seems strange to be upset at they/them usage for an unknown entity.
I doubt anyone would be upset at people using he/him when referring to Satoshi, but also along those same lines, it seems strange to be upset at they/them usage for an unknown entity.