Remember this is Japan. They still have a great deal of traditional thinking in Japan and children, especially female children, are often extremely obedient to their parents, older siblings and those socially above them. All of this also tends to support the students going along with whatever they are told. In addition the school allows all kinds of sexual conduct (in itself often enough to make most teens simply sit back and have a good time) and it is an elite school that presumably produces strong academic graduates even if they don't end up excelling as sex-slaves.
With 50 or 100 students per year graduating, not all will be sold into sex-slavery, possibly only 10%, or else the market would be flooded, so I presume that 80-90% of the schools students have a normal and successful school life and go on to work in successful positions at Morimoto Corp.
And Zaer is right; according to the anime ALL the students are children of Morimoto employees who owe the company something.
Snake, imagine your character in Reina's position, in charge of this whole set-up, then see it from her POV, See? It makes total sense to have the students under secure control with no way out other than to obey what the Governess wants from them. If they don't meet the grade for her designs they just graduate anyway, but you have to have that family incentive to keep them there.
Also in the anime in episode 5 we saw the graduates at work servicing politicians, industralists, financiers and entrepreneurs at an evening's event at Reina's mansion. Almost all the girls seemed to love it!
I think Nile is okay with your character, Snake, if you were to add in the part about his brother that I suggested. Then we're good to go. Is that right NileGoddess?