I'm sorry, but for some reason I can't believe you.
The program currently pays per family, tops, R$ 306. Minimum wage is more than double. I don't see why mentally and physically capable people would refuse the opportunity of doubling their income.
Some can make more by taking informal jobs, which they don't have to report. With that, they are locked into a local maximum. And I've heard anecdotes from social workers of people who do prefer taking the "free" money to working. When you are dealing with hundreds of thousands of families, there will always be a few outliers.
The program currently pays per family, tops, R$ 306. Minimum wage is more than double. I don't see why mentally and physically capable people would refuse the opportunity of doubling their income.