Big waves are crazy powerful.
Then there's the speed, wizzing over choppy water on a board feels like driving over a very pot holed dirt road, the chops SLAM into the board over and over again. You lean on the rail to turn and the board may just drop away into a hole or get slammed up by chop.
And if you fall, you don't penetrate the water, you just skim over it like a flat stone (or a rag doll in the mouth of a dog, shaking it from side to side)