Probably cause people don't know or don't care to know because theyd rather have the carat size over quality. That way a poorly cut larger stone is more affordable and can cater to those customers. Then the well cut ones are the customers who are willing to pay the premium for the cut and don't mind the loss of rough. Even if an angle change would only take away .05 carats that could be the difference between .95 or 1 carat. Some people would sacrifice the cut to be able to say that have a full carat... Regardless if the .95 stone is the better performer.