That and the constant travelling never actually resting properly sleep all over the place constant mental and physical stress just chucking more and more painkillers etc inLet's not forget aside from roid use that even though wrestling is scripted the pain is real.
Especially in the wwf days when for instance they would use legit steel chairs, take head shots, cut themselves for blood effects, etc.
That takes it's toll on the body as well.
Easy to blame the gear when it's very little to do with it