Tag, i saw this thing on daily planet or some shit where they took them off. It's not that it would snap but it's a possibility and they don't want to risk it. One chick took it off and could barely hold up her head.
It's not that their necks are long, it's that the metal coil pushes the rib cage down, giving the illusion. The fact that they can barely hold their head up is because they've had those things on since they were babies, so their neck muscles were never really in use, and they gradually weakened.