I can explain it. It's just partly subjective. For example, it may be influenced by the current culture, fashion, etc. (for example those epochs when people like more obese people; the obesity was an attractive trait; there are even some nowadays' societies where the fat people are considered beautiful.) But there are inherited taste (aesthetics) preferences (tests with babies shows that they like the faces that most of us consider pretty and they dislike the ones that we consider ugly), so when it's about some average person (4/10 - 6/10) you can see some people will say he/she is handsome or pretty, some will disagree but when it comes to those "edge cases" -- 1/10 - 2/10 and 9/10 - 10/10, there already will be almost no exception: probably 99%+ of the people will do agree that the 1/10 and 2/10 is very ugly people and the 9/10 - 10/10 are very attractive people.
Some visual examples:
Let's say that the first woman is 1/10, the second is 5/10 and the third is 10/10. If you ask boys, almost all of these boys, around 100%, will say that the first one is ugly, some of the boys will like the second one and some will not like her, but most of them (around 99%) will like the third one.
The same with the males' faces:
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As that one said, once you pass the certain objective level, then the subjective choice plays role.