If the figure part is already in production at some level, then it's cheaper to use an existing piece rather than mold an entirely new one. One need look no further than this pic:
The chipping paint at the swivel-arm battle grip belies the red plastic underneath. Simply put, this is a hand painted 87 Jinx figure used to show how Vypra would look. Hasbro then took this figure and used it in the box pic.