Just found out have antibodies for herpes never had an outbreak or symptoms why is that?

Subclinical Infectio. One can be infected and mount such a good immune response that the infection never has to chance to damage the body. This is called a subclinical infection. The blood test will show that immune response.
Immune response. You were exposed to the herpes virus at some point (most people are). When that occurs, plasma cells in your blood create antibodies, which are chains of proteins that help your immune response mount a more effective defense if you are exposed again by binding to the virus. Immune cells then recognize the antibody coated invaders and attempt to destroy them.