Back in February, the U.S. said the following at a DSB meeting:
Rather than seeking to make revisions to the text of the Dispute Settlement Understanding to permit what is now prohibited, the United States believes it is necessary for Members to engage in a deeper discussion of the concerns raised, to consider why the Appellate Body has felt free to depart from what WTO Members agreed to, and to discuss how best to ensure that the system adheres to WTO rules as written.
Along the same lines, U.S. trade lawyer Terry Stewart recently wrote this:
Requiring the Appellate Body to revisit claims of overreach in cases where one or more parties have raised that claim under clarified rules of the Appellate Body's role could be possible but unlikely without an understanding of why the Appellate Body has felt at liberty to disregard the limitations within the current DSU and ensuring that such disregard doesn't continue.
They are asking "why" the Appellate Body has felt free/at liberty to depart from/disregard the agreed rules. I feel like it is implied that they have a theory about what went wrong with the Appellate Body in this regard, but they don't say what it is.
My own view is that the Appellate Body has been doing its best to interpret the WTO agreements in a way that conforms to the rules, but opinions vary about interpretive approaches and the meaning of substantive rules (and also, people make mistakes), and as a result there have been outcomes that people disagree with. That's inevitable with any adjudicatory process.
But the critics seem to think that there is something out of the ordinary that happened with the Appellate Body. I'd really like to hear more about what they think it is.