If you study for a specific kind of test, you usually limit the knowledge that you gain out of the material in the class. I think most students have a false sense of the importance of knowing only what's on the test. There is too much emphasis on grades and not enough on true scholarship, searching for knowledge out of interest, not out of benefit. If academic concerns are the issue, I agree that a test file could help those individuals study by providing sample problems to people as a basis for undermining the important topics covered in class. However, I think this would involve more than just collecting old tests and providing answers.
Most professors provide sample tests for the purpose of emphasizing topics.
There is a concern that if tests aren't updated they could become outdated, etc. I understand the idea behind a test file, but I think it strays from the purpose of what would be considered academic concerns. Old tests seem to be used by a lot of students as indicators of the limited amount of material that they should know. The best answer that I've heard is when the professor simply repeats the name of the class. A mass email was sent via the dean of undergraduate students office to all the students in the Engineering school.