My first guess is that no one wanted to insult/offend an amputee that wanted to ride.
Everyone, at least most of us, want to accommodate and encourage those with handicaps.
He was an adult; he wanted to ride; and not being much on physics knowledge I would not have guessed that mostly missing legs would have made him fly out of a shoulder harness.
There was NO shoulder harness. Plus amputees were given a list of do’s and don’ts before leaving the hospital and high speed roller coasters were on the don’t list.
However,he showed very poor judgment getting on such a ride;and the family member assisting him showed equally poor judgment.
Personally,I believe riders should be strapped in like a 4-point racing harness.
But then again, personally,I don't do roller coasters.