The problem with giving people free money, is it reduces the incentive to work. Australia, and other countries, have introduced systems with minimal requirements for receiving welfare: making an effort to find a job, based on simple objective criteria.
That's more or less the situation in the US at present, as I understand it. We all want people doing useful things, but this kind of system 1) means that the benefit of finding that job (for those at the bottom) is substantially less than it is under BI, and 2) we're requiring people focus not on their job search or on preparing themselves for work but on documenting their job search and jumping through bureaucratic hoops - hopefully there is substantial overlap but when do we ever measure exactly what we intend to?