I make about twice what the median American makes and I still have plenty of things (mostly a house) I could use more money for and work hard to get more money to get those things.
You can sure well bet that I wouldn't quit this job to live off of $10k a year work-free.
And if I was working part-time at McDonalds, I sure as hell wouldn't quit that job to live off of $10k a year work-free, instead of working AND getting that $10k/year and enjoying all the better quality of living that would afford me.
My mom lives off $10k/year because of disability, and believe me, it is a terrible existence. Even though she's disabled and isn't supposed to be able to work, she still wants to, because she needs more damn money. Of course, with disability, if she gets any job at all, even one paying minimum wage for an hour a day, she loses all her benefits. With a basic income, people like that would be allowed to work to better their lives, unlike with the perverse incentives current programs offer.