We have a process to ADD states?
Why don’t we have a process ( albeit with HIGHER THRESHOLDS ) for sates to LEAVE if a super-majority of people within them WANT to leave?
I know people sometimes say we fought a civil war, which set the standard that states cannot secede from the union.
As you note, there is no procedure for states to leave the union.
I have wondered sometimes, if any state voted to secede, would a president nowadays use military force to keep such a state in the union? Lincoln did so in the 19th century, but would a president today do so?