Spite. I've seen big players (controlled by pissed off influential person) chase down small businesses in my country relentlessly, to the point that the father of a family had to serve in jail for 2 years because he couldn't afford the fines. The lawsuit lasted 3-4 years and the poor guy was called to court basically every month... It was awful to watch.

Eventually some good souls gathered the fine money and bailed the poor man. And then the suers got pissed and tried to raise the fine, eventually had to pay for... I don't know the legalese for that, but basically they took it too far and the judge called them out on it and forced them to cover ALL legal expenses.

My point however is that for ordinary people even the nerves and time lost in a lawsuit are too big a price to pay. We aren't machines, these things get to us.