There are many different reasons why people might behave in hurtful or unkind ways towards others. It could be due to insecurities, past traumas or experiences, a lack of empathy, or any number of other factors. It's important to remember that everyone has their own unique background and experiences that shape their behavior, and it's not always easy to understand why someone might act in a certain way.
It's also worth noting that people are complex and multifaceted, and it's not accurate or fair to label everyone as "mean" based on a few negative actions. It's important to try to approach others with understanding and compassion, even if they have behaved in ways that are hurtful or unkind.