False. It was actually Reagan in 1988 that finally gave reparations to Japanese-Americans.
https://en.wikipedia.org/wiki/Civil_Liberties_Act_of_1988
So you're wrong about taxpayers at the time paying for anything. It was taxpayers in the late 80s that paid for injustices committed by the US government 40 something years earlier. I'm sure most of the taxpayers in 1988 were not of voting age during WW2 when the internment camps existed (where one could make the argument that voting age adults at that time implicitly approved of the injustices committed by the US government against Japanese-Americans). And for what its worth I don't know why the taxpayers being alive when the incident happened matters. Taxpayers didn't directly commit the incident. It was elected officials that decided mistreating Japanese-Americans was a good idea.
So if the Japanese-Americans can get reparations 40 years after the fact, why can't black people get reparations 150 years later? Why is 40 years your arbitrary cut-off? And don't give me anything about slaves no longer being alive to collect what they are owed. The impact of slavery goes beyond the life of the slave. It has impact the lives of his and her descendants for generations. It is still felt among the descendants of slaves. If the promise of 40 acres and mule had been honored at the time, black people would have had access to generational wealth in terms of land ownership that could have totally changed the destiny of most black peoples lives living today.
Denying the descendants of slaves access to restitution for hundreds of years of free labor is an injustice. If that labor had been compensated to slaves at the time, the reality of life for black people in this country would be radically different. Black people might have actually had wealth they could have passed down to later generations.