Liu Kang is the focus of the movies and cartoons because he's the focus of the games. He's the protagonist, the one who is usually scripted to defeat the main villains and win the tournaments.
And the Great Kung Lao(the ancestor) is important to the backstory of Mortal Kombat because he prevented Shang Tsung's tenth consecutive win, which would have allowed Outworld to invade Earth. Even before they introduced Outworld in Mortal Kombat II, he was there in the backstory of the first game, where it's mentioned that he's a Shaolin fighitng monk who was defeated by Goro, which caused the tournament to fall into the control of Shang Tsung.
Im really lookin forward to season 3. But I dount it'll happen since it hasnt yet. Really hope it though! And yes,I hope they bring Kabal in with those Awesome hookswords! But this is the wrong tourny for him to show up.