But the Constitution explicitly vests that power in the Congress. Why are so many people, who ordinarily get worked up when they perceive Constitutional violation, ignore the plain meaning of the Constitution's text? I will quote it again one last time.
Fifteenth Amendment to the United States Constitution
Even the reactionary 5 on the court can't deny Congress this power. They go about it saying that the methods Congress chose to effectuate this Constitutional command "worked too well" so it's now "outdated."
But then obvious question is: How does the court know that? Does the court have such capacity and competence to make that call? The answer is no. And in any case, that judgment is Congress's to make
per the Constitution.
Edit: And I also note (again) how little Roberts has to say about the 13th, 14th, and the 15th amendment of the U.S. Constitution in his opinion striking down Voting Rights Act. It seems as if the conservatives on the court wish those amendments didn't exist.