1) Because you're nice. Nice people don't finish last. Maybe in high school this was the case, but in the grown-up real world, nice people will definitely have more chances of finding and staying in good relationships. No one wants to date an a-hole or a b*tch, so stop trying to be one, karma will bite you in the ass.
2) Because you don't have an "amazing" job". A good person will love you for the person you are, not for your job title. And if that is what they care about, you can tell them to buy a one-way ticket to the island of "forever alone because I'm shallow".
3) Because you don't have the "perfect" body. First, the perfect body does not exist because it is completely subjective, meaning everyone has a different definition of what the perfect body is. Second, that means that for some you DO have the perfect body. Third, everyone is attracted to different things, and it's definitely not only about physical attraction.