Polishing a turd might be an appropriate description of the last ditch vinegar boil after you’ve already racked up 10-12k hours.If the point of the vinegar is to unmask the catalyst by dissolving .mineral depositation, what does the boiling really get you? I had similar results when I boiled my ceramic one (I was initially pleased but I got a new cat a couple months later anyway).
Are you asking why boil it vs. just soak it in vinegar? I just followed the directions. Don’t plan on ever doing it again based on the results. Masking might have been removed but whatever causes a cat to wear out must not be masking.