Getting final exam answers ahead of time is a form of cheating. To cheat is to take an examination in a dishonest way. Therefore, if you get those answers dishonestly, you get them by cheating.
The purpose of a final exam is to test your knowledge, and the questions on a final exam are designed to do that. Getting the answers to those questions ahead of time prevents this from happening. In addition, the consequences for cheating may include an automatic zero for the exam, immediate failure of the class, suspension or even expulsion, depending on the school's or college's policies.