It’s the redistribution that you’re missing.
300M * $20k does equal $6 trillion but it is returned to the tax payer who stumped up the $6 trillion.
The 50M who aren’t contributing tax represent an actual cost of $1 trillion. The remaining $5 trillion is redistributed.
250M people contribute $20k. 300M people receive $16.6k.
300M * $20k - $6 trillion == $0