Why are ear symptoms associated with tm joint disorders?

Pain, tinnitus. Tmj problems can be associated with ear pain in the associated ear which can radiate to almost anywhere on the same side of the head. Tinnitus (ringing of the ears) can also occur.
They are related. The back of your jaw joint is the front of the ear canal. Many of the structures that pass into the ear pass through the back of the joint. These are arteries, veins, nerves and ligaments. Therefore, there are structural, functional and postural correlations between there structures. Also many of the muscles that help move/support jaw movement refer pain to the ear region. (referred pain).
Referred symptoms. The TMJ (temporomandibular joint - jaw joint) is right in front of the ear canal. Pain in the joint can be referred to the ear (similar to pain from a heart attack being referred to the left arm). Popping or grinding noises in the joint can sound like they are from the ear.