Maybe he thought you were taken, since you did not show him any interest. It could also be that you have a scary personality and that is why nobody approached you. I would advise you to ask some of your friends about your personality and see what you can do.
why ponder on it - it could be a number of reasons but i will say because you are so beautiful that they are intimated and taken back -- so just go and you will probably enjoy it more and just think your options are Wide open and it is politically correct to go alone these days and shows that ones who do are more stronger and independent then the others for they are their own person and dont need anyone else to lean on
Simple answer, you already had a guy picked out (but he couldn't go) now nobody will cut in because they don't want to make him mad. You could try asking this guy to find you someone to "chaperon" you to the dance or ask any dateless gay guy to take you.