It’s cost. Multiply population by the amount and you get a huge number. The math only works if you get rid of a lot of others social programs with vested interests.
There are about 250 million adults in the US. If we give each of them $1000 a month, that's 3 trillion dollars per year. For comparison, the US government collected 2.6 trillion dollars in federal income tax in 2022.
And then imagine that the 2.6 used to include things like hospitals.
Sorry buddy, you get the $1000 a month but you no longer get medical care or disability benefit or buses. It’s all gone. Don’t you feel better off now that everyone is equal? (The rich obviously still get to go to hospital)