There are many reasons why we care what others think of us. From what science understands so far there are a plethora of reasons, everything from environmental, how your were conditioned as a child to your DNA. What science has seemed to agree on so far is not as broad.
Some of these reasons are:
We want to be liked and accepted. We are social creatures who crave connection with others. We want to feel like we belong and that we are valued members of our community.
We want to be respected and admired. We want to feel like we are seen as competent and capable individuals. We want to be seen as someone who is worth listening to and taking seriously.
We want to avoid disapproval and rejection. We don't want to feel like we are being judged or rejected by others. We don't want to feel like we are not good enough.
We want to maintain our self-esteem. Our self-esteem is how we feel about ourselves. It is based on our own thoughts and feelings about our abilities, our worth, and our place in the world. When we care about what others think of us, it can affect our self-esteem. If we feel like others don't like us or respect us, it can make us feel bad about ourselves.
It is important to remember that not everyone will like or respect us. There will always be people who disagree with us or who don't appear see us as we see ourselves. But that doesn't mean that we are not worthy of love and respect. It is important to focus on the people who do love and respect us, and to not let the opinions of others affect our self-worth. One's own value or worth as a person, that feeling of being good enough, of being deserving of love and respect affects how we feel about ourselves, how we interact with others, and how we make decisions that are most beneficial for ourselves.