That depends. A lot of people try to find self worth in the feeling of superiority, which is what I feel like a lot of “popular” high school kids seek. This translates to them treating others poorly or them being nice to you in an extremely insincere way. It doesn’t always mean that they are  assholes, it’s more that they will do what they need to do to remain popular or to become popular. Some “popular” people are nice and authentic, but I have found that to be a rare occurrence. In order to be popular, you need to place value in the opinion of others (at least at my school). Usually, the people who care so much about what other people think are insecure and try extremely hard to look cool or pretty or whatever they think other people would like. In order to place so much value in theses surface level qualities, your character has to lack in substance to a certain extent. That’s just the way I see it at my high school, and I’m sure that every school is different in what defines being “popular”.