My orthodontist is not fixing overbite? im am adult. why?

May be best for you: Your orthodontist may have determined that either correction of your overbite would require jaw surgery ( and the risk/benefit ratio is not favorable), or that extraction of teeth to address the overbite problem might be detrimental to your facial profile and/or jaw joint and dental health. Your orthodontist is in the best position to answer your question based upon your records. Ask him/her.

Growth: Since you are an adult you are no longer growing skeletally. Overjets are much harder to correct in a non-growing patient. They can be corrected to a smaller extent with slenderizing and consolidating excessive space.

Could be skeletal: We find some people that large overbites are due to their lower jaw being to small. We are limited to how far back we can move teeth and must keep them in the bone. Also as the teeth go back so does the lip this can give the impression the patient is wearing an upper denture.

Talk to them: There is no reason i can think of why they wouldn't but they may have their reasons. Ask them.

Ask the Orthodontist: Perhaps you also need surgery. Perhaps there's a reason why overbite correction is being delayed. The only way to find out is to ask your Orthodontic Specialist (hope you're seeing a Specialist) who knows your case best.