Does a minor sin become a major one if a person's bad deeds outweigh their good deeds, or is there another reason for that?

Persistence in a minor sin transforms it into a major one, for there is no minor sin with persistence, and no major sin with seeking forgiveness. An abundance of sins, even if they are minor, may lead to perdition. Nevertheless, the door of repentance is always open, and sincere repentance erases sins. As for one who dies affirming the Oneness of God (monotheist) and has sins upon him, his matter is subject to the will of Allah Almighty.