Because they’re psychosomatic and many representations of Christ on the cross show the nails through the palms.
That wouldn’t work, though, they’d soon rip right through flesh between the metacarpals, and the victim would start flailing blood everywhere (supposing they were properly tied to the cross) or drop to the ground. They’ll last much longer through the wrists, lots of small well packed together bones, there.
The NT kernel is built on top of a hardware abstraction layer, which should make it easier to port it to different architectures.