I wonder... is this a serious question or a witty question with a humorous answer?
To me, nice guys finish last because they let themselves get taken advantaged of - and if it isn't that, it's because the scum of the Earth loves to roam in packs, work in packs, and kill in packs... in this manner, the nice guys are obviously outnumbered, outskilled, outsmarted, and outmatched in almost every way.
Hardly does a lone "bad" guy get away with what he's doing for long, he/she needs connections, needs company, needs someone to watch out for them.
Nice guys? ...people would LIKE to watch their backs, but they just never do - they turn their head away and refuse to see that their own "bad" kind is doing this to the good man.
Being nice has no flaws, it's just that being mean and bad has so many advantages.