There are guys out there who prefer big girls, and ones who don't have a preference and are willing to date thin, chubby, big, whatever.
I think that one of the main reasons why it seems like a lot of guys don't like bigger girls is because of the social pressures surrounding it. Media and society tells us that thin is attractive, fat is not. This leads to both men and women believing that a woman has to be thin to be attractive or appealing. Not all people buy into this. Some guys are open about their attraction to big girls. Other guys are attracted to big girls, but aren't willing to admit it/to date big girls because they're worried about what other people will think. Keep in mind too, that this site is mainly frequented by younger people who tend to care more about what their peers will think.
I think that for a lot of bigger women who don't get much attention from men, it's not necessarily because they're big, but because of how they let their weight affect them. Many big women tend to be shyer or keep to themselves more because they are self-conscious about their weight, or because they are bitter or scared to open themselves up to people due to being mistreated because of their weight in the past. Also, sometimes bigger women might not take as much care in their physical appearance (dressing nicely, doing their hair nicely) because they feel like there's nothing they could do to make themselves attractive to men and so they give up trying.
You seem to be the opposite of this---outgoing, friendly, take good care of your appearance--which makes you more approachable.
Lastly, there are some guys who simply aren't attracted to big women. They may be shallow, or it might just be a preference (we can't force ourselves to be attracted to something we're not). For others, it has to do with stereotypes about weight and health. Fat is generally seen as unhealthy (though obviously thin people can be unhealthy too and weight isn't necessarily the best indicator of health). For myself personally, I'm attracted to people of all sizes, but if someone's weight prevents them from being able to enjoy an active lifestyle with me (I like hiking, going on long walks, bike riding, rollerblading, etc. and I want to be with someone who can share these things with me), then I'm probably not going to be attracted to them.