To this day I have no idea. I even unreasonably suspected that, for whatever reason, my Apple ID had been blacklisted. I reached out to Apple and they said that I wasn't. It's actually interesting... Now that I think about it, I can't even make in-app purchases without contacting Apple Support and making them validate it. Some really weird stuff. My Apple ID is OLD though - it's a first gen Apple ID. But I'm not sure if that's the issue. I'm also not sure that the IAP issue is even related.
I could just try the pre-preorder with my new, secondary ID - since that account is as clean as anything - and just pray that it works. But if it doesn't...