Because that will fail to detect a program that halts in X+1 time. The problem isn’t to detect if a program that halts halts, the problem is to generally create an algorithm that will guarantee that the analyzed program will always halt given an infinite time running on an infinite computer.
While I agree with you in principle, in practice I feel everyone agreed it really only had to be one state. There was never a chance this didn’t go to the Supreme Court and rather then duplicating the effort everywhere, it will be decided there.
Now if the Supreme Court decides this is in fact up to the states, I would then expect significantly more states to take the steps to remove him knowing their ruling will stand.