Not because we actually hate the United States or want to leave it, per se. But because we're tired that:
Our states frequently are among the best in quality of education, healthcare, social mobility, personal income, civil rights, environmental protections, etc. and produce more income to the federal government than we take from it.
And yet the Southern and Midwestern states prefer to constantly try to tear down the systems we've proven work best, and complain about paying taxes themselves even as they drain our taxes to sustain themselves via federal funding without which they'd be broke.
So I say, let them find out what it will be like without us propping them up, since they ungratefully hate us so much.