It is just a cleanliness standard. It is not required. I spent a decade in the details of automotive paint. I only covered the surface basics for paint. What I call clean for paint is an order of magnitude more dirty than a surgeon, and they are orders of magnitude more dirty than a silicon chip foundry. When it comes to making plastic stick and look pretty, an automotive painter might be helpful for framing the scope of what is possible. All I can tell you is I have a Prusa and never have these problems, so I explained my experience and methodology as to why I do as I said. Again, sorry this upsets you.