Low self steem and or competition. A girl want to show that she gets the prize even if she does not like it. Nothing wrong, word or advise choose your battles, you can't go on life fighting for something of somebody that you don't even want it. Waste of energy. :D
They just like him too much to let them go
They just feel jealous of each other and wants to outdo others to get what they are, that's how competitive this society is. You must fight to get what you want.
I don't know I kinda do the same, I don't want to see a guy I have chances with to be with another girl!
Because SOME girls are so attracted to someone that they don't care what the boy says. Trust me my exgirlfriend did the exact same thing, she realy wanted me back, saw me hanging out with one of my good friends (girl) and went ape shit.