Now if this wasn't a visual novel there'd be no issue. A live-action film with the following description would be fine:
"A film that aims to raise social awareness of child and school related social issues through a story about four troubled heroines who, under unexpected circumstances, join forces with a young hapless teacher to fight against the evil forces that mean to exploit children."
Visual Novels (and to a lesser extent anime) just have a very seedy reputation in the west.
There's also the artstyle to take into account. I'd imagine that they took on an artist who worked on erotic loli stuff, because the artstyle in-game is pretty much in line with the non-H CGs in eroge VNs and non-H parts in 3D h-animation.
I mean, the artstyle has pretty much established itself at this point, so if you pick up a VN artist whose expertise is children...
I WON A BET AGAINST AZUREN! WOOOOOOOOOOAAAAAAAAHHHHHHHHHHHHHHHHHHH