Most countries give so many tax rebates to low-income individuals it's essentially UBI. Welfare, food stamps, unemployment insurance, lowest taxable income level. The $1,400US/month Germany is proposing is less than their minimum wage of $11US.
They have to fill out complicated tax forms (really, a tax preparation company fills it out and takes a cut) to get rebates like EITC. They have to spend time visiting government offices to renew their food stamps. They have to be subject to relatively invasive life inspections for welfare- and 'workfare' programs that require people to leave their house, put their kids in daycare, and rake leaves for 8 hours a day are always going in and out of fashion, with over half the states usually implementing a form of that program under some name.
I feel like if it were my choice, I'd like to get a little less money but have it 'guaranteed' without a bunch of time obligations that would interfere with my attempts to raise my kids, learn a skill, or get a basic job. Of course, 80%+ of people in the USA who are in poverty are children, carers, disabled or the elderly, so it's not like they're learning a new skill or trying to find other work. Their time is still valuable though.