Most helos hang under the rotor like a bucket hangs from its handle. You can swing the bucket around under positive g and even take it upside down without spilling the contents.
Now try to make the bucket STAY upside down - just doesn't happen, was never designed to do so. Same with helicopters.
Even on the ground, negative pitch will make the blades cone down, and that would be disastrous for a lot of tail booms and people under the disc - an S76 is low enough at the front as it is.