Because when a woman gets rejected, or a man breaks up with her, she thinks she’s not good enough.
Women tend to set their eyes on a man, and think because they like that man, that he must be exactly what she wants, which is why they will complain all the time, but stay with us. Or we tell them straight up that we don’t want a relationship, and they think if they keep smashing, we’ll eventually catch feelings. (It happens sometimes, but it’s rare) Then, when we don’t change for them, they think they’re not good enough.
They think their happiness is dependent on being with a particular person, regardless of that person’s attributes. And they don’t want to go through the process of finding and getting to know another man.