But when you get a black mark against you it seems like you get stuck in an administrative blackhole where nobody is authorised to tell you WHY or they themselves don't know.
It was the same way with the no-fly list for the longest time too, but because that wound up impacting a few powerful Americans it was eventually sorted so now you can at least fight it a little or do additional background checks to get off of it.
The worst part is that these security black marks seem fairly easy to get: family member or friend a "terrorist?" Share a name with someone "bad?" You're now on it. And nobody you can actually talk to can either tell you why or has the authority to remove you.
I would blame it on bureaucracy, but that is an easy out for a policy which is partly intentional -- Americans don't want people visiting, working, or studying on their shores. They have made that abundantly clear over the last ten years.