The only failed attempts I have seen have been as a result of using other liquids or medications to complicate the digestive and Chemical reaction process. I think this is just random human error. Interesting observation though if it is mostly males that have made the error, but I assume that is mostly coincidence.
The biggest factor is likely body weight. I for example am 5'6 and 112 pounds. The standard dose is likely a little bit excessive for me, but better safe than sorry. The other side of that would be someone who is very overweight. If you had an adult that was 300 pounds for example it is logical that they would need more than a person who is 112 pounds, but in the end a fatal dose is a fatal dose. That's why it is averaged at 25. The range is something like 18 to 30, so 25 is a good round number that basically covers all the bases. Personally, if I were obese I would probably up it too 30, but I think having too high a dose would cause more pain and potential complications.