Why don't doctors test for genital herpes or genital warts unless symptoms are shown?

Lot of positives: Genital herpes cultures and wart biopsies (if needed) are often obtained when you have an actual lesion. They guide if you need treatment and confirm diagnosis. Blood tests can identify if you have had exposure to herpes (genital or oral) as high as 80% of americans can test positive by blood tests without symptoms. You dont treat history of exposure.