Exactly. That is why using BMI in isolation to determine if you are overweight or not is a bad idea. Two people can be approximately the same height and weight and have very different body types which would keep only one of the two from fitting in a ride vehicle.
I wouldn't exactly call having height, weight, or size restrictions "fat profiling". The more extreme the forces that act on a body the more likely there will be more restrictive requirements. Since I was not on the design team, which is good for everyone involved as I am no engineer, I imagine that the restrictions are as high as US or their underwriter would allow without taming the ride, and that isn't a good option either. There is always going to be a trade off on extreme rides, look at Cedar Point.