It's simple, though. The more players who get back for the final chase, the better chance they have of beating the chaser. Not just that four heads are (mathematically, at least!) better than three, but they also get an extra head start per person, so they start on four steps instead of three.
So, the fourth player takes the minus amount in an effort to ensure a greater chance of getting back for the final chase, thereby affording the team a better chance of winning an albeit reduced amount than winning nothing at all.