Why doesn't cbt or systemic desensitization work well for flying phobia?

Often it does: Actually those are the most successful strategies that exist! Perhaps you did not find a therapist who works well with you. That is a very big part of the effort. A coach at a gym can also make or break a training effort depending on how you work together. Don't give up. Look for a good fit!

VRT for Phobias: I have been very successful in eliminating the fear of flying with VRT. Phobias and anxieties respond well to Virtual Reality Therapy(VRT). VRT is exposure therapy in a safe environment. The research suggests VRT is 90% effective. Seek out a therapist who uses VRT in your area. You can find providers through www.psious.com, www.limbix.com, or www.virtuallybetter.com.