Exactly.
Sicle Cell Anemia sounds like a great thing for the men who suffer with it but in most cases it does not turn out good. Priapism is a major component of this disease. In some cases men have erections for more than a day. Some have erections for hours. Some have erections for even longer. The duration of the erection will determine how much damage is done to the penis. A man who has an erection for a day plus will gain mega size but it will be rendered impotent in almost every case. The men who hold erections in less time turn out to be very lucky and rare but even these may suffer some eq issues. I would say Shane Diesel is a good example of someone who's priapism has greatly effected his size but he also suffers with weak erections. The same thing applies to Tony Duncan and a few other 'larger' performers. You will see them gripping the base of their penis to retain blood in their penis. Then there are the rarest of the rare, men like Mandingo (not sure if he does or not but let us take it as an example) who may have had the luxury of 6-8 hours of erection daily that did not effect anything but the size of their cock. They still have great eq and they have a massive penis.
Men, here, have tried to mimic this for years, including myself with crap results. It is very difficult to retain an erection for the length of time necessary to cause megaphallus without destroying tissue.