Poor people are making economic decisions not to come out ahead but to mitigate their losses. They aren't doing this because they want to, it is because it is the best decision they can make given their constraints. For example, they can either sell their time for minimum wage, far less than the value they create, or they can starve or go homeless. The person they are selling their time to knows that the alternative to taking the deal on the table is pain or death -- that the poor person cannot walk away from the bargaining table without making themselves worse off. So they are free to ignore the value those people create and, instead, offer the least amount possible for the poor person to avoid the fate they'd suffer if the walk away from the deal. In a word, exploitation.
So, the poor person makes a deal that looks terrible to people who have the luxury of being able to walk away from a potential trade with no loss. People that must be enticed, that must leave the table with more than they brought, people who are on an upward spiral, who do not generally have to make a deal or face loss. People who are used to all parties leaving the table with more value.
They are, as much as any human can, making the best decisions they can in their situation.
Are there people that are simply too dumb to figure out what is best for themselves? Yes, but that number isn't anywhere close to the 45 million people we have living below the poverty line in the US.