The main cause of a cracked tooth next to a wisdom tooth is more related to an abnormal blockage of the wisdom tooth. Because the blocked wisdom tooth does not have a normal adjacency to the adjacent tooth, and because it is located on the very back of the mouth, it often makes cleaning more difficult and can cause deeper decay in the root of the adjacent tooth, which can lead to root cracking or root fracture.
Wisdom teeth can also cause topping of adjacent teeth, causing resorption of the adjacent teeth and making them less resistant to external forces, which can lead to cracking of the tooth when the bite force is too great.