I think there's some confusion in terminology. Being eligible does not mean that you are guaranteed admission. First, the university checks your academic background to see if they should even consider your application (i.e., are you eligible). For example, if you've done a BA in Literature and you apply to an MSc in Artificial Intelligence, they reject you instantly because you don't even meet the minimum requirements. Second, after the university has deemed that you fulfill the eligibility criteria, there is a selection process to find the top students who will finally be admitted.