why do some filmmakers work with girls who clearly don't want to be there?

[nightowl]

i can sort of understand that really beautiful girls continue to get work and contracts even though their sexual performance is pretty poor. there will always be a market in terms of guys wanting to watch the most beautiful women get fucked, even if they are regular cum dodgers, look about as excited as if they are doing the laundry etc. my own personal preference is beauty and performance. she's got to be good looking but also fuck like a slut, willingly take a load of cum in her mouth etc. however, what i don't get is why some girls who are fairly average in looks and even worse in performance continue to be used. i don't know the ratio of girls available to films being made but it seems there's a lot of girls being used again and again who just lie back and take it without even the slightest glimmer of emotion on their faces and then keep their lips tightly sealed during the cumshot before rushing for the box of tissue.