1. The Civil War was fought in part to prevent the South from seceding and continuing with slavery.
2. It would be too expensive. Regardless of the fact that taxes paid by citizens of a seceding state were used to build federally funded infrastructure such as freeways and dams, the feds will declare that they will need to reimbursed for the full current value of all federally funded projects within the state. No state could afford to pay the price tag of secession.
3. It wouldn't be Constitutional. The Declaration of Independence isn't the Constitution.
4. If Texas, or some other nominally Republican state, made noises like they were going to secede, all of the other Republicans would start making huge gestures to keep Texas in the fold lest the Republican candidates in the remaining US become unelectable at the federal level.
5. When given a chance to take the red pill or the blue pill, most people take the blue pill. Most people have way too much drama in their workaday lives to want to add secession to the mix.
6. Most states already sold their souls to the feds. What state still has a bonafide militia that compares favorably to the federalized National Guard? What state really wants to take over the full cost of ownership of federal lands? What state wants to give up its share of the highway fund? What state is capable of maintaining dams and levies without the aid of the Army Corp of Engineers? What state is capable of supporting all of the welfare programs that much of their corrupted citizenry now depend on? Yes, if somehow a state succeeded in seceding its citizens would no longer have to pay a federal income tax. But would the politicians have the will and the ability to instantly raise the state taxes to meet the demands of all the freeloaders in their borders?
Thank you all for your thoughtful replies.