It isn't about buying happiness.
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It is ultimately about reducing the overall cost of social services. 
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There is an old saying: "If you think education is expensive, try ignorance."
This problem is quite similar.  The cost of poverty comes in many forms.
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People with no income are inordinately expensive from a social services perspective.  They are far more prone to require emergency medical services, rather than using a GP.  They are far more likely to impose first responder costs - whether police, fire or ambulance.  They are far more likely to find themselves entangled in the court system, and, ultimately, in some form of detention.  They are far less likely to get out of the poverty trap by finding and eventually holding steady employment.
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It does not require very many hospital emergency room visits or 911 calls to the police to add up to $17,000.  The public cost of arresting, trying, and jailing a single person, for so much as 1 day is almost certainly more than $50,000.