Why are some girls so insistent on hanging out with guys who they don't want to be with?

[Hikari]

In other words, why would a girl so desperately want to spend time with a guy who they aren't romantically interested in? Someone they have already friend-zoned? Even if it's painful for the guy, but he's too weak to say anything? Or even if the guy has a girlfriend, and doesn't find it appropriate to be hanging out with other girls one-on-one? Why do some girls get upset and take it personally when the guy in either scenario finally puts their foot down and says they can't spend so much time together anymore because it makes them uncomfortable given the circumstances?

I'm a girl, and I had really good guy friends who I lost contact with because they got girlfriends or realized I didn't like them the way they liked me. And I was fine with that... I mean, I still cared about them and went to the trouble to find out how they are doing in life by facebook and through other friends. But I didn't confront them or get emotional. My attitude was simply, "it is what it is". I'm satisfied even if the only contact I share with them aftewards is a simple facebook reply on my wall to a status update or something.

Knowing that the people I care about are alive and doing well is honestly enough for me. So why would a girl get all upset if a guy tells her that he can't hang out with her as much anymore? Or if he does hang out with her, it has to be in a group with other people, otherwise it gets too uncomfortable for the guy?

I don't understand women sometimes.