This is exactly why I use a custom skill - I can tell it what to focus on, I can give it a ill formatted blurb of why I'm making the changes, and it will format it nicely, and add more context based on the changes.

Most of the time, the PR descriptions it generates for me are great.

I think the issue is you're assuming it's always a poor output, which isn't the case. I'm in a much smaller team than you'd expect, so the why is talked about sync more often than not, and it becomes less of an problem.