SD v. Dole is different. First, the state could've chosen to go without that money, which is a fair choice, according to SCOTUS. Congress can't "tak[e] absolute control and [tell] states" what to do, or how to do it. See New York v. United States. That's a general principle. However, the VRA is quite different, because the Fifteenth Amendment specifically empowers Congress to enforce the Amendment on the states.