Someone living in NJ could easily be offered a tax increase from a state lawmaker, feel that there is a benefit to them in the service that tax will pay for, do the math and realize that with the SALT deduction, they wouldn't be paying any extra money in taxes for their services. Changing the SALT deduction is what changes the math here.
They weren't voting for "higher taxes" they were voting for "more services".
Now the law has changed where, regardless of state, your federal tax burden remains the same. It leveled the playing field and states will have to adapt and lower their taxes, otherwise risk losing residents to states where tax money is better managed.
The assumption that the tax money is poorly managed is a misrepresentation. They aren't just lowering taxes, they're also going to be cutting services (or finding new revenue streams). Assuming the states lower their taxes to bring residents in line with their previous combined tax bill, is it realistic to expect that these states are going to get the same funding for the same types of projects from the Feds? No. So while it's "leveling the playing field" it's also a kick in the dick to states with higher State/Local tax levels and forces them to scramble.
But hey, look at all those Florida billionaires flush with cash that they're going to trickle down on us now...
This is a confederalism vs federalism issue. If you believe in a strong Federal government, support the lowering of the SALT. If you believe that states are best at determining how to support their residents, oppose it.