LU, everything you said about seminary in Israel is true, it’s an experience that is life changing and wonderful.
But there are some girls whose parent can’t afford it- think about how much it costs, x however many girls there are in the family.
Also, some don’t feel it is right for a single girl to be on her own, far from her family, even if in a supervised dorm. Some girls grow and mature, and some don’t handle the freedom well.
Mostly, chasidim feel that way and don’t send their daughters to learn in E”Y.
These are legitimate viewpoints, and girls shouldn’t be made to feel second class if that is their circumstances.
If more girls stayed, there would be more options in the US, just as the options in E”Y have expanded with the increased demand.