The proof is that agencies that do require them almost never require a specific major. Get it in anything and that’s fine. Imagine walking up to an accounting firm with a degree in history or university studies and getting hired straight in.
They respond that it magically confers some sort of air about the person that makes them a more wholesome cop.
But at 3am you want the other kind of cop coming to save you.
By requiring a degree as an initial filter, HR avoids discrimination lawsuits.