Timeline doppelgangers...

[STB Sgt Reed]

The dumbest thing is that Present Liu Kang and Kung Lao didn’t have to fight their younger self if the theory of “if past character dies so does the present one” really works.

They could potentially WANT to kill their past selves to eliminate themselves from ever becoming revenants in the first place. Basically allow themselves to go to the afterlife with the Great Kung Lao and all their ancestors or whatever.

OR

If they allow young Liu and Lao to succeed they couldn't rule the netherrealm or whatever evil shit they like doing these days.