
Why are the sisters in these manhuas ALWAYS nasty and evil. Willing to betray and torture their kind for the sake of men.
And why are the men so fickle and foolish to prefer these type of women?
Is this a cultural thing?

It's a recurring trope I am noticing. Especially the behaviours of the fathers willing to discard their partner and children for the sake of their new lover and even prefer the children that aren't even theirs but their step children??
To the extent the father physically abuses and humiliates their child in front of their new spouse (to the spouse's and their childrens' glee).

I think it's because of the authors' lack of imagination. They are like "we want a tragic background for the MC, what do we do?
If it's a male MC, usually they go for killing his parent or sibling and rarely for a bitchy treacherous sibling.
If it's a female MC then bitchy sister and bitchy stepmom 99% of the time"
I'm sorry, a story of this calibre does not need 70+ chapters...
Everything that is in "Popular manga" doesn't need more than 50 chapters :P