A block grant is like giving a transfusion in the right arm using blood taken from the left arm and spilling a lot of it in the process. A net loss.
Federal overhead for managing the money taken from the states to be given to the states wastes quite a bit of the money being transferred. And there’s also the money that must be spent to monitor (aka control) the recipients’ use of the money.
We clearly need more prisons and prison guards one way or the other.