if someone has to take the job, why can't it be me?
Because you haven't demonstrated a propensity for excellence in the chief factors which determine whether or not you'll actually get one, your GPA and LSAT. If it COULD be you, you would have done better in those two categories. Barring some incredible life change, you will likely graduate law school in the exact position which your GPA and LSAT predicted you would (i.e., not a good place).
but what do you have against anyone believing in themselves.
I don't have anything against "believing in yourself". In fact, I believe self-confidence and motivation are crucial to success at anything. However, there come a point where confidence and self-assurance turn into wide-eyed optimism, arrogance and dilusion. For example, I am a good chessplayer, but I know almost for a fact that I will almost certainly never become a Grand Master. I still have faith in my skills, but I also know where my limitations are. I don't believe, however, that you know where YOURS are.