That would ruin the fun of winning. If people spent hundreds of points, or empty their entire bank account, to win a game, only to always profit in the end, then that would make winning boring and lame.
I'm not one to say that players should earn profit all the time, that's what every ZS player is working towards every map, but humans rarely win on ZS. A victory on any map is a rare moment where even if you're down 500 points and in the negative, you'll find enjoyment out of contributing to the team in some way when you win in the end, and that's fun.
No offense, but like many point-whore ideas I've seen suggested for Zombie Survival, this sounds like another idea made with a point-whore mentality.