They Hold Drastically Different Values
It’s no secret that the “United States” is no longer united and hasn’t been for a very long time. Every election cycle is a battle of two kinds of voters which couldn’t be more different. They have different cultures, views on politics, religious beliefs and overall different world views. This incompatibility could end up becoming violent, and many would say it already has.
Secession could be a peaceful solution that both sides can support. The progressive parts of America would be free to implement their socialist policies, and the more conservative/libertarian parts of America would become beacons of freedom and prosperity once again.
The people of California, Washington and Oregon seem to be coming to this conclusion.