It is not their job to enforce federal laws, but they are actively thwarting federal law. Both through refusals to notify the federal government about criminal illegal aliens being released, refusing detention holds, lawsuits against building facilities, lawsuits blocking arrests, etc..
pedantic. You can use lawsuits, within the law, to thwart the law. You can do it knowing you will lose, just to cause delays, like Califorinia and the 9th circuit are ACTIVELY doing to slowdown gun control cases from reaching the supreme court where they 100% will be struck down. Refusing notification is an action.
Why should it enforce a law from a separate sovereign entity, is the question. And the answer is, it shouldn’t. I don’t think states do, or should, enforce federal anti-discrimination laws. The feds do that. The states pass their own anti-discrimination laws if they want something to enforce themselves.