when they posted that question they were hoping people would rate them well. those questions are either for assurance or for fishing for compliments, if they dont get the results they want some may get offended. in short, some just want to listen to good things and not prepared for honest feedback.
I understand what you are saying and I agree but if someone wants to know what others think about their physical appearsnce, its not necessary to be mean. All thats necessary is "I dont find you attractive, I give you a 3/10." Its not necessary to say "I find you putrid. You could scare the buzzards off a shit wagon." They didn't ask to be offended, just rated.