Some people can take a business goal and figure out how to turn it into a clear spec.
Sometimes these people are programmers.
However I know programmers who suck at this and I know non-programmers who don't.
As an aside, I'm getting a bit tired from the "programmers vs product/business people" trope. The average software engineer would be nothing without a good product manager in my experience. And going by this thread, there seems to be at least as much contempt from programmers/software engineers for product people than allegedly vice versa.
The average software engineer doesn't have a good product manager, he has an average product manager. They still get things done.
I think dividing work into programmer/UX/product manager is an actually huge regression.
Software is of lower quality today and requires far more do-overs than it used to. As someone who liked working closely with customers and making decisions in all these areas (for their benefit), it has made the entire career far more of a slog than it used to be.
Also, I find these endless internal cyclical conversations to be much more draining than actually writing code. Looping over and over with planners and ideas folks isn't energizing like actually writing the product is.