Because moon dragon is garbage. Star Dragon gets used, mainly because it's hard as nails in combat, and can't get cannoned off. S6 can be reached by quite a few armies, and S5 is quite common. However T7 is a big number, meaning most often your getting wounded on 6s.
Star Wars Legion - Rebels
Guildball - Alchemists
Blood Bowl - Lizardmen
Guildball - Alchemists
Blood Bowl - Lizardmen