'Single' women are not single
When I meet women who were cheated on or trust was broken, and then constantly talk about how they don't need a man, they come off as not single at all.
Not only is their ex still in their mind more than a healthy person in a relationship would think about their partner, but they see this man in every man they see.
They let this ex partner craft their attitude, their views towards men, literally their entire life.
So on paper they are single, but mentally they are more in a relationship than anyone else, hence their defensiveness.
Similar case can be true for men who were cheated on