Same with mortgage applications and other gatekeepers. No matter how much you have your ducks in a row they will always ask for something to show they did their due diligence. It's helpful to leave out something obvious and easy to produce.
This control of access to resources is where the name comes from, and its broader use (rather than the highly specific social use we see online) is recently exemplified in the EUs Digital Markets Bill describing large search providers (like google) and social media (facebook) as gatekeepers.