I think you are the only one to complain... so it must be you! Dont know of anyone expecting traction on a shifter! Could put a stack of o rings around it with a really tight one on last or maybe a piece of hose slipped over it for more bite.
The Cannondale shifter was one of the first OEM ones that was made of aluminum, folding and Cannondale kept it simple with no bends. I just think no one thought to improve on it. It is such a simple design, I'll bet you could find something that fit and was tricker looking if you tried.