It’s curious that the country/federation that introduced the concept of self-determination doesn’t allow self-determination for its constituent states.
Individual self determination.
If a local majority secedes every time it wants to trample on a minority, or in the case of the civil war, an oppressed majority, two things happen: one, politics devolve into fractured feudalism. Local elites have a mechanism for wresting absolute control. That, not the Constitution or a Bill of Rights or elections, becomes the basic unit of power.
Two, our two-plus century record of peace on the homeland shatters. Every election or court case found unseemly by a contiguous local majority prompts a Twitter and existential crisis. Foreign adversaries hammer the wedge and split the nation into warring vassal states and too-small-to-matter opposing countries.