This is FUD. We have no idea the reason why.
Given it was never marketed, it's possible perhaps despite the feature being exposed it never worked correctly and AMD saw fit to just disable it rather than people get a false sense of security through it.
the fact they won't tell us why is the concern.
"no one uses it and there is a bug" may invite more questions or panic, but "that's all we're going to say" implies that Mythos found something scary, or that the NSA demanded they all get turned off.
AMD is spreading FUD by not answering why it was removed. They could stop this in its tracks if they wanted.
Why call out FUD when you only have more/different uncertainty to offer?
Spreading misinformation is different to suggesting possible reasons.