Someone once asked...
Someone answered with kindness...
There are many reason why. In a capitalist society, it's beneficial if the population are unsatisfied, it leads to more purchase, using money as a therapy. We are also not taught to love ourselves. We could have introduced that in school and culturally, but instead we are trained to be unsatisfied with who we are.
Another soul answered...
You think you should be someone else, and can't accept that you are not. Understand your limitations.
Another soul answered...
Because you aren't aware of the beautiful traits of you have, and the potential of your future you. Someone judged you in an incorrect way (that someone is also you) and you are believing those lies.