I think the major reason is that there is very little competition. According to rumors a certain previous monopoly still makes it very difficult for getting permission to give out student visas, and giving cheaper tuition rates at private schools.

As stated earlier it's not very difficult to lower tuition if you work out some sort of deal. But beware most schools will say anything to get you on theirstudent visa. Some, especially that previous f'n monopoly canmake it very difficult to switch to another school later.