Throughout his teenage years, Draco was in a relationship with a witch named Pansy Parkinson. Apparently, J. K. Rowling hated the kind of girl this character represented, referring to her as the "anti-Hermione." She said that this kind of girl reminded her of the people who used to bully her at school. Therefore I think she probably thought this sort of character didn't deserve to be written into the finale of the series.