Your point about "directly informed and refined by customer feedback" is well-taken, but in my experience a large backlog is rarely that, but more a dumping ground that seems daunting. Of course it depends on who is managing it and how, but more often than not I've seen PMs succumb to big backlogs rather than make it a well-vetted list maintained proactively like you have stated.
By the way, I enjoyed the article! It's a good share, and appreciate the perspective.
Dumping details into something that we can’t understand yet seems like it smacks of a way to manage anxiety. Kind of like an inverse form of procrastination.
It’s easy to believe that we can just think our way out of problems, but sometimes we need to build small things, solicit feedback and iterate. And that can be uncomfortable if there’s something impeding that.
I think maybe the implication is that if your backlog is big, it's a "smell" that you're over-planning. I don't think that's true, but I guess the sentiment is good.