Why wouldnt my doctor discuss end-of-life issues with me?

Many possibilities. Some doctors don't feel comfortable, some don't have the communication skills. But you can find another doctor or clinician who can answer your questions, so do not give up! This is not about you...
They need to... If your doctor, for whatever reason, will not discuss end-of-life issues with you, you need a medical professional to speak with about this. There are doctors trained in palliative care who are excellent people to speak with.