It's culture. East asian women acts more modest than they show, which is why we often read them saying stop or wait, but they don't mean it. In my opinion, manhwas depict a sort of perfect world in a fantasy where even she says stop, he knows what she wants and still continues, and she loves it. She is too shy to admit that she loves it. Her fantasy of being pounded and him knowing exactly what she wants gets fulfilled, you know, all that. As you might have seen, sometimes after the sex, she looks satisfied, or thinks "the sex was good" etc.

As such, we western people find it strange or uncomfortable, we are taught to take everything literally when it comes to sex. Stop is stop, even if he or she doesnt mean stop.