Presumably they take your driver's license mark-of-the-beast and submit it to the surveillance bureaus to check that you're not an undesirable, just as stores do with non-receipt returns for store credit.

It's not like it's the front line employee's or location manager's idea to informally record your identifiers "just in case" - at the very least it's a deep corporate policy. And the company didn't whimsically conjure up that requirement on its own, but was prompted to do so as part of implementing some kind of third party surveillance solution(s).