About the logic/direction of plot...

I ve read the raws and the logic of these characters is very confusing/tiring.
Some vague spoiler since I don't understand Korean:

Enemies turns into friends/allies, friends turns enemies, enemies turns friends again, all enemies to each other put their difference aside due to a bigger mutual threat that was caused/created by one enemy etc....
What I find very incomprehensible is:
Characters forget that this one vampire enemy (the maker of the vampire MC), invaded the save haven for humans with her entourage, killed those who resisted, enslaved them, did whatever she want with them like in any dystopic zombie dictatorship, as a scientist she turned/transformed the brother with cancer of the FL into a psychotic zombie puppet master before the outbreak who is now the power hungry main antagonist, was defeated by the antagonist and left barely alive. And the human characters didn't take the chance to finish her off. Probably because she still has the useful scientific knowledge of how to solve the whole zombie problem. What the hell was she doing when she ruled the human survivors in a shopping mall??? So she gets a big pass, occasionally abuse the Vampire MC and gets treated like a normal ally who is NOW doing her work to find an antidote/serum. In the latest chapters she is suddenly being portrayed more calm, less bloody arrogant and sadistic and she tells her story how she as a naive loyal servant of a shitty king was sired by an old mysterious vampire centuries ago....

WTF!!!
Can you understand why I am so bothered by the constant plot twists?!
It's like a soap opera for horror action thriller that gets just more complicated through the appearances of characters that are all somehow conneteced to each other and reveals shocking truths one after another...