It's a question that most people are scared to ask because it rocks the boat; self preservation leads most people to avoid doing that, as you never know who might fall off.
I remember reviewing a product backlog and wondering how the prioritization was done. The highest value stories did not appear to be at the top - nor the smaller stories that might give the "biggest bang for buck".
Then I noticed it was stacked with requirements from our most "vocal" customer and the most recent requests. Essentially whoever nagged the Product Manager recently got their requirements moved to the top.
On another project - it was clear that the Business Analysts didn't understand what they were really asking for. They were copying and pasting requirements from an existing list. There wasn't much analysis going on.
When this occurs - it doesn't matter how good your delivery team is. You need a good Product Owner.