Serious question for discussion: Please explain to me why women cannot simply say "NO, STOP DOING THAT, I DON'T WANT TO DO THIS" and then remove themselves from the area, when faced with unwanted sexual behavior

On my last thread on "Yes Means Yes", I raised the question of why it is that women can't seem to just "say no" to unwanted sexual behavior. I don't understand why a woman cannot simply say "No, I don't want you to do that" and "STOP DOING THAT" when some guy is coming on to you.

I do not understand the usual protests that

1. We need to be nice about it because the man might get violent

and

2. We don't want to look like bitches

and

3. Men should just notice that it's unwanted without us telling them directly.

Intended for open discussion and questions for all:

Help me understand this. Why can't women just say no? Why can't women just be direct and say you're not interested and then leave? Why can't women just say "NO STOP DOING THAT I DON'T WANT YOU TO DO THAT" and then leave?

What is so hard about telling a man that you are not interested in him sexually? What is so difficult about telling a man you don't want to date him? Is there something difficult about telling a date that you don't want to fuck him?

Is there something different about 21st century women from late 20th century women, that they could say "NO" and then leave; and somehow, today's modern women are somehow unable to do this?

Legislated consent, as in "Yes Means Yes", infantilizes women. It says women can't take care of this themselves. You need men, men you won't fuck and don't know, to take care of consent for you because you cannot be trusted to do it yourselves. (I don't believe this personally. I give women much more credit than this.) Is this what today's women believe? Is this what 21st century women (and feminists) want to say about themselves?

Why can't women just say "NO" to men they're not interested in, and leave it at that?

EDIT: This thread is not about men's responsibility to not rape/assault women. That's a given. This thread is about women's responsibility to be direct, clear and unambiguous about what they want/don't want, and their responsibility for being in situations with men they don't know all that well. Please stay on topic and answer the questions I asked without deflecting to personal attacks and "why can't men not rape women?" THAT IS NOT WHAT THIS THREAD IS ABOUT.