Welfare isn't UBI. Give everyone the same amount and you'll have a hard time convincing the people earning 70k to vote against another 12k... That's the secret formulae.
People earning 70k will vote against "another" 12k if it reduces their taxes by 16k. That money isn't free—a minority will see a net benefit, with everyone else footing the bill. If you're earning 70k then you're unlikely to end up on the "net benefit" side of the equation.