They don't really need it to be honest. I think the joints would be an eyesore. The real issue is the posture or position they chose for the legs. They gave him this completely straight, locked knees position, which is a very odd choice. The Gamorreans never seem to stand in a straight up position on screen, they're always sort of hunching, knees bent.
Like I said, Sideshow made some very strange choices with this fig, which is why it's almost there but not quite. The posture of the legs needs to be fixed, the neck, or lack of, needs to be fixed, the odd wrong colour britches, the flat paint job etc. I'm confident, with some modding, if I ever get around to it, they can look really great.