A country recognizes that the rate of company creation has gone done (or some similar metric). They identify the tax rate as a reason for this. They want the tax rate to be lower to ameliorate this. They leave the agreement.
Now presumably there are penalties or such in place for this type of agreement, so it would need to be weighed as onerous enough to accept any such penalties. If it is just one country that feels this way then it might be a non-starter, but if the global minimum tax gets to a point where many countries feel this way, it would probably be viable to coordinate to leave the agreement all at once, with the remainers having little power at that point.
Now presumably there are penalties or such in place for this type of agreement, so it would need to be weighed as onerous enough to accept any such penalties. If it is just one country that feels this way then it might be a non-starter, but if the global minimum tax gets to a point where many countries feel this way, it would probably be viable to coordinate to leave the agreement all at once, with the remainers having little power at that point.