Girls, Why do some girls get angry when a guy doesn't want to stay friends after she rejects him?

Disclaimer: I notice this doesn't apply to ALL girls, hence the "some" in the question title.

I do think it is possible for guys and girls to be friends. Hell, around 70% of my friends are girls. However, I develop crushes on some (≅ 10%) of my female friends. When I build up the nerve to ask a female friend out, I nearly always get "I only see you as a friend." To be clear, I RESPECT THIS ANSWER. I know that I'm not entitled to girls, and that she has every right to reject me. That's not the problem; the problem is that girls will usually get mad when I don't want to remain friends after that.

Romantic feelings don't just go away because the girl isn't interested. Those feelings take weeks or months to die out. If I hang out with a girl I have romantic feelings for, knowing that it'll just remain as a friendship, I feel a great deal of inner-turmoil. Perhaps I am just not mature enough to deal with these feelings properly.

How come so many girls get pissed when I tell them this? Nobody is entitled to my friendship, nor am I to anyone else's. I feel like breaking off a friendship with a girl who rejected me is the best thing for both of us. I seriously want to understand why some girls feel like they are somehow entitled to a guy's friendship.
Girls, Why do some girls get angry when a guy doesn't want to stay friends after she rejects him?
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