New Jersey, one of the most impecunious states in the union, was behind this week’s Supreme Court ruling overturning a federal ban on sports gambling. Not sport fans or sport leagues: It was the work of a leading avatar of the blue-state governance model, in which public-sector unions and politicians join together to ratchet up unsustainable spending and debts.

In the days since New Jersey got the legal go-ahead to bulk up its coffers with sports betting, the urgent job of the major sports leagues has been to simulate pained...