I am currently applying for a mid-range private school that teaches the carrer I want primarily (software engineering) and a prestigious public school for computer science(it doesn't have software engineering). So if I make it into the public university, I would evaluate between the specific carrer of the private one and the economic help of the public one, and choose the most appropiate one.

The thing is, when I was reading their entrance rules, I saw that if I decline my vacant after being admitted in the public one, I could not apply for it for the next two admission processes(at two per year, that means a year and a half). What is the philosophy behind this? It benefits the student, giving it more schools to chose from. And it also raises the funding because of the payment that is done to give the entrance exam(which is not one of the things public schools in my country can brag about). And it doesn't harm anyone, because the next one in the list would enter. The only colateral damage I can think of is extra administrative effort, but a year and a half vetted from applying to the university because of that seems to much for me. So, why?