The reason it does so is that it's the only viable way to fund it. 235,715,590 people 21+ in the US. At $13k/year that's just over $3 trillion dollars per year

The reason it does so is that it's the only viable way to fund it. 235,715,590 people 21+ in the US. At $13k/year that's just over $3 trillion dollars per year. Social Security spending was $888b in 2015, Medicare spending was $546b in 2015, and other welfare spending was $1.031b. If you cut all SS, Medicare, and other welfare spending and redirected it into a $13k/yr UBI, you'd still be about 20% short of your necessary funding. Total federal revenues for 2015 were about $3.25t. If you leave Medicare and SS in place? You could only fund 46% of the UBI requirement with existing welfare spending. Good luck passing the massive tax increases needed to fund that. And that's ignoring the fact that the SSA indicates that the long-term ability to meet SS obligations is already in danger.