Why do girls treat their guy friends badly while in a relationship?

[Anonymous]

A girlfriend wanted to visit me today for a hangout. I made tea and some snacks for the evening. But she stood up, after like an hour late she told me she can't come, she was talking with her boyfriend and got lost in time.

Just to be clear I am not interested in her romantically but have seen girls doing similar behavior before. What happens to keeping promises and being nice?

[Guy13]

Because they are stupid OR do not realize that it is much more difficult to find a reliable and like-minded guy friend than a piece of ass... I think you may benefit from communicating this to her... more gently of course ;-)