Tactics. If they take the matter to the USSC and lose then they do not have any legal way to resist other states from doing the same thing. They could only threaten procedural and financial penalties for passing such laws.
The admin is going to go after blue states. Just like the soviet union not allowing anyone to leave. They need to hold those votes.
The Supreme Court has already upheld a voter ID law from Indiana. So the concept of voter ID already passes legal muster from the courts.