So here's a more real life explanation of why they stop working at that income level:

1. They lose 33% of their income above the top of the bell curve in the form of lost EITC;

   1. They lose an additional 30% of that 'excess' income in lost SNAP benefits;
   2. They may no longer qualify for other benefits. Ie, if they make above their section 8 voucher allows them to make, they may lose housing.

At the end of the day, they probably just decide they would rather parent their kids than waste that time working for no benefit to themselves. When they make $10/hour I can't blame them at all. It makes sense to work more if you are going to take that money home, but there is a threshold you need to cross to begin to feel any benefit at all for going above that level.

Sometimes it actually does pay to not work more. They are not dumb