They were all doofuses. How else could you explain getting trapped on a lush tropical island with an old rich guy, a science geek and a fat bald guy and still not get any from either the actress bimbo or the farm girl?
Also, science geek figured out a way to charge the batteries for his radio, but couldn't figure out how to make a raft out of all the palm trees and vines? If the barbarian headhunters could figure out how to get to the island, surely seven civilized people including a seasoned navigator should be able to figure out how to get off.