To make a short explanation;
When people use no blue eyes, the downgrade rate is kinda low, maybe attempt 5 times and still no downgrade. When enhancing and you want no downgrade, they should use blue eyes. It's fairly easy to enhance stuff without using blue eyes and not getting a downgrade due low downgrade rate. People should use all 3 bundles to ensure the no downgrade will be caused. Not betting on it since the rate is low, which some people might do or are doing perhaps.