Typical 'every women is bisexual' stereotype
These sitcoms like this play on this stereotype that just because a girl is attractive and wild that she somehow can be attracted to other women if tempted. The writers need to turn this around think to themselves, "Hmm... I'm a straight guy, if I got really close to my good friend, would I go gay for him?"
I think in reality, some women will kiss other women at parties just to get attention, and some women really are lesbian, but are in the closet for societal pressure reasons.