Most Helpful Guy
Well take a step back and think of someone who is nice, kind and friendly but you just have no desire to be involved romantically with them.
Most Helpful Girl
Because you're they're best friend. You never acted like a potential love interest in the first place. Friends are supposed to know their friends and be attentive to their feelings, that's what friends do. It doesn't give you the assumed right to be seen as their ideal type.
If you don't make it clear that you are more than a friend then it's your own fault if you get treated like one. Also you have to accept that you don't get to decide what they should find attractive; you can be nice and all, but that doesn't make you their type. They get to choose that.