What pro breeders are you talking about? Throw out some names to back up those statements.
Some females never reach 1500grams, does that mean they shouldnt be bred? Im sure there are 1200gram females put there that lay healthy 4-6egg clutches every year. The snakes wont ever get any bigger than this. Same way that not every female will reach 3kg+. Not all get that big.
Obviously humans are different but thats like saying theres a certain weight that women should get pregnant at and they cant before they reach that weight. Or saying that EVERY girl is sexually mature at the same age. Some girls just "develop" sooner than others. This isnt the case with humans and isnt the case with snakes. They all grow and develop at different rates and if they arent sexually mature they wont lay for you. Same way if a girl isnt sexually mature, well, she cant get pregnant.
*In no way am i condoning teen pregnancy, just trying to use easy examples lol*
EDIT: Also im guessing he lost part of the clutch due to the fact that he was not ready for eggs and didnt know how to properly care for them or the babies once they hatched. Once again, just a hunch.