Many do not like themselves. There are a lot of hypotheses why that is so. These two articles may enlighten:

A Discussion of Self Hatred
When You Don't Like Yourself | Psychology Today

In the first article, ALLAN SCHWARTZ, PH.D., references the work of Theodore Isaac Rubin, MD and Psychoanalyst, who in turn " ... borrows from a great psychoanalyst of the mid twentieth century, Karen Horney. Rubin:

Dr. Rubin reduces this formula down to two selves, the Actual Self and the Real Self.

Actual Self: Who we are with all of our talents, limitations and illnesses, both physical and psychological.

Real Self: The illusions we believe in about who we should be, in terms of being wealthy, powerful, lovable, independent, etc.

To the extent that we hold onto illusions about our Real Self is the extent to which we reject our Actual Self and feel self hate.

We must accept "... who we are instead of wishing to be something or someone else ..." leading to compassion. "[To] be compassionate to others, we must learn to be compassionate to ourselves." Compassion for self and others means we must end self-hatred.

In the second article, Alex Lickerman, M.D., concludes:

Treating others well, it turns out, is the fastest path to a healthy self-esteem. If you dislike yourself, stop focusing on your negative qualities. We all have negative qualities. There's nothing special about your negativity, I promise you. Focus instead on caring for others. Because the more you care about others, I guarantee the more in turn you'll be able to care about yourself.

The key is to accept ourselves and give to others. We must do the work.