First off, the #MeToo movement is a form of standing up for oneself - but in a collective manner less likely to bring about reprisals. In this instance, the "bully" is a social system where sexual harassment has long been tolerated. Secondly, expecting a hundred pound 5 foot tall woman to be able to fend off or stand up to a 6'2 guy who is 250 is absurd.

In addition, many times the perpetrator has a position of power that makes "standing up for oneself" pointless or even dangerous. Go read the story I've already linked you on reprisals to better understand that.

In the US military (where 38 men are raped every single day - and a lot more women than that), the perp is often a superior officer - the person you are supposed to report misconduct to. Instead of getting help or justice, the victim ends up getting further punished.

Might makes right is a messed up belief system on a lot of fronts, one of them being the way that it blames victims for not being able to protect themselves.