> And similar proposals like the Negative Income Tax would cost far less money and have none of the presented downsides.

Most people file taxes once a year, meaning they would get this payment once rather than monthly, which makes a huge difference if living on the poverty line. Similarly, many people making less than the minimum for filing [1] likely don't file their taxes. This was an issue with the child tax credit as well -- you want to get resources to the lowest-income households, but doing that with tax credits means you don't actually reach those households, meaning you still have to introduce new programs to reach those people [2]. There were proposals to make that tax credit into a monthly payment but IIRC they did not pass before the child tax credit was ended in 2022.

[1] https://www.irs.gov/newsroom/who-needs-to-file-a-tax-return [2] https://www.vox.com/22588701/child-tax-credit-accessibility-...