Reminds me of an experience I had at church. Every Easter I worked with others to prepare Easter breakfast. Year after year I noticed the dishwasher silverware basket had a bad bacteria smell that never went away. Made me wonder why good smells fade and bad smells last forever. Like you said, someone posted on a forum that it is nature's mechanism to detect the bad. In this case, bad bacteria. If the bad smell faded, it would be a health risk. I threw out the basket without even asking for permission to do so. Good smells do not last and that will keep the fragrance companies in business.