How come girls say you're "such a nice guy", and then won't date that "nice guy" that is good to them?

Anonymous
for example my good friend has this girl who pretty much relies on him for emotional support when ever she's having issues with her boyfriend or whatever and always tells him he's such a good friend. don't get me wrong I'm not saying I don't think girls can be good friends some of my own best friends have been girls however I know because I've talked to him about this that he wants to be more then a friend with her and its oh so obvious she has put him in the oh so dreaded friend zone. so my question really is why is a nice guy who is always there for a girl not ever thought of as a potential relationship? isn't that what people want ? someone who is reliable and is there for you when you need them?
How come girls say you're "such a nice guy", and then won't date that "nice guy" that is good to them?
7 Opinion