Wouldn't the reasons for requesting identification be the same those for banning people - the system has flagged that you might be from the wrong location/under 18/creating multiple free acounts etc - so is validating.

They request ID for bans so that they can ban you personally. ID checks may as well be a sign that you've already been banned and they're fishing for ways to make the ban harder to evade. Venmo does the same thing.