This is purely my opinion but it pretty much covers me and all the males I know like me. I could be described as "nice", what I actually am is weak. I'm so weak as a male I can't even get females interested enough to be friends with me. Of course, being a fat bastard doesn't help but I know guys fatter than me who have loads of female friends.
We "nice" guys hope that a girl will see us, notice we are gentle, no aggressive, maybe a little shy and we hope she then goes on to do all the work for us when it comes to starting a conversation. Why the hell would a girl interested in a mate waste her time on someone who lacks the balls to even speak to her?
You can be a gentlemanly, charming guy who doesn't act like a dick and still get women, if you have the bollocks to back it up. You have to show that you are the master of your own world, that you are happy with yourself and that you don't give a fuck what people think. To those of us who lack the self worth to feel that way, we see guys that have those traits as jerks.
I can't take my own advice, I'm a lost cause but if you like a girl for fuck sake let her know about it. You can never be "too nice" as the girl said to the OP, what she really meant was "you're not manly enough for me to want to fuck you". The interest was obviously there, she went on a date with you. How you acted on that date simply showed her that you wern't fucking material.
That is what it all comes down to at the end of the day. A relationship without sex is simply a friendship, so if a guy or a girl brings out the friend card, it means that you're a nice person to be around but you lack whatever quality it is they are looking for to bump uglies with. For men at least, that quality is strength. Whether it's a talent you're good at, you don't care what people think so you cover yourself with tattoos, you get out on the dancefloor and make some shapes, or you have a wallet full of money and a nice car, those are all displays of strength. This comes even before looks, but it's something people don't even realise they are looking for because it happens at a subconcious level.
That doesn't mean be a dick, I can't emphasise that enough, it means make yourself an alpha male. In a pack of wolves or a troop of chimps the one who stands around at the back not wanting to get in the way or isn't strong enough to fight for a higher place in the chain will not get to mate. Humans are no different despite how much we like to think we are.