Why do some girls refuse to share information about the guy they dated?

My BF never tires of telling me that his ex GF was the most exquisite person in the bed. She even went skinny dipping with him and gave him BJ without his asking for it. He even told me that she once booked them in a hotel that had mirrors on the ceiling. I find it odd that a girl would do so far to satisfy her BF. I know this girl and she is very conservative. I called her and asked her to confirm all this. She refused to speak to me. I find this disgusting. I think girls should share these details so that guys cannot fool girls. If I break up with this guy and he tells vile things about me to others, I won't like it either.