Even so, if they hit up the victims for $100 instead of $10000, they'll need to send out far more letters, and deal with far more targets who simply ignore the letters. IANAL, but I believe it does cost money and time to actually file a lawsuit and/or compel the targets to do things like pay up under penalty of law.
Note that in the majority of cases, they don't file a lawsuit. Their business model almost certainly depends on that. You're right, of course, that their volume would have to increase, but I'm not ready to immediately dismiss the notion that their current tactic is not the most efficient.
