Exactly, what matters is the enforcement, which is the job of the executive. Courts have an easy way to deal with legislative nullification: declare the law unconstitutional or preempted and be done with it. Courts do not have such an easy way of dealing with an executive.
Also, a state has no affirmative duty to help enforce federal laws. It can even do things to oppose the federal law's purpose. Nullification is when the federal law is declared null and void, which is not the case in any of those.
Example: South Carolina can announce that they are firing all their tax collectors and will not contribute to collecting the 47% tariff on imports. South Carolina cannot declare that there is no tariff in South Carolina and no one can collect it.
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