Liu Kang, Kitana, Sonya Blade, Jax, Kenshi, Sub-Zero, Scorpion, Smoke, Jade, Kung Lao, Nightwolf and Raiden...oh yeah, Johnny Cage too.
Shang Tsung, Quan Chi, Mileena, Kano, Noob Saibot and Shao Kahn.
Characters like Baraka, Reptile, Ermac, Sindel, Kabal, Cyrax and Goro were not included due to them often bouncing back between alignments within the franchise.
While Mileena was depicted as a heroine in New MK1, she has been largely depicted as a villain in almost every one of her appearances.
Also, while Scorpion has been depicted as an anti-hero or villain (sometimes unwillingly so), he is largely on the side of Earthrealm within the conflict of Mortal Kombat, hence why he is on the heroes picture.