Because the SCOTUS has already ruled three times before that it doesn't.
The standard is that a minor error that would not have influenced the trial outcome can be overlooked.
In this case, sentencing outcome; and in this case, the issue before the Court is whether this was indeed minor.
However, Certiorari should have been denied as it wasn’t SCOTUS worthy, and granting Certiorari and then ruling against makes it all the more harder for somebody else to raise that issue - perhaps in a more applicable case.
It was SCOTUS worthy, because a Federal court and a Federal appeals court had already ruled against state courts clearly covered by the AEDPA, and because the Supreme Court needed to establish a precedent. See my previous post on AEDPA.
You’re correct on all points. I misread something that lead me to believe that SCOTUS upheld a lower courts ruling that it didn’t matter. Thus I felt denying Certiorari.