Because they sure had all the rights their ancestors had fought and died for.
They didn't have one right that they had fought for and the Northern states had agreed to. That was the return of runaway slaves. As you no doubt know, there is a clause in the Constitution that addresses this, but Northern states had been flaunting it for years and disobeying the Constitution. The Supreme Court ruled that some of the Northern 'personal liberty' laws that prevented the return of runaway slaves were unconstitutional. Northern states were practicing nullification just like South Carolina had attempted years earlier over tariffs.
Without the runaway slave clause, the Constitution would never have been signed in the first place. The North later backed out of their Constitutional duties. Who was it again who was telling the country how it should be run?