I don't perceive an increase in bi activity as signaling any kind of lack. I think the activity may be born of the freedom of the environment and encouraged by the obvious interest of onlookers. There are a couple of women I am just as comfortable with as any man. The nifty thing about interacting with them is that the interaction alone will heighten arousal in others. Why knock it?
I'm probably one of those women who can engage in bi play, but when with the male, loses all track of my female counterpart. That awareness is lessened if she happens to be one in my strike zone. Is that a bad thing? Depends on what you're looking for.
If the definition of bi-female is "a woman who can have a sexual experience with another woman and enjoy it," then I am a bi-female. But for the same reason that I won't engage in sexual activities with every man, I won't engage in sexual activities with every woman.