Hrothgar:

Crucifixion was actually a favorite pastime of the (pagan) Romans and other more civilized nations. While it is prominently mentioned in the Bible, it was not actually recommended or "officially" sanctioned by the Jewish hierarchy.

   I think that had something to do with its labor intensive nature (it takes a fair amount of carpenter's time and exectuioner's labor to actually crucify someone) and the fact that it was a bunch more expensive than simply picking up some good-sized rocks and casting them in the direction of the condemned.