BS here,
The 180 isn't about the relationship, it's about the BS regaining strength, confidence, and to start the detachment process. If a couple is in R, and the WS is remorseful, there would be no need for the 180.
However, if the WS is cake eating, fence sitting, still lying, withholding facts, etc (in other words, not remorseful), then the BS needs to start detaching from the situation. Talking about the relationship, the A, asking again for something from the WS, etc all can keep the BS 'stuck' and it's very unhealthy.
The 180 is to begin the process of detaching from the situation, the A, the WS, the relationship. Again, it's not for R.
Now, one side note - there are thousands of cases where the 180 has actually snapped the WS out of 'the fog'. You see, as the BS begins removing themselves from the life of the WS, and is no longer obsessed by the behaviors of the WS, or the details of the A, the WS is forced to realize that this isn't going away, that the BS will NOT be treated like an afterthought, that there is a very real chance that the WS will end up in divorce court, BS gone from their lives, kids seen part time, etc. In other words, it shows the WS exactly what they are losing because they begin to lose it. In these cases, the WS that 'gets it' based on the BS detaching will often begin doing what's necessary to heal the relationship.
I mention this because many believe the 180 is a tool to snap the WS to their senses. It's not. It is 100% to help the BS begin to see that there is a world outside of the A, the marriage, the actions of the WS. Can it have a positive affect on the marriage? Yes, but that is NOT the goal, and it shouldn't be the goal of anyone that is using this very effective technique.
I hope this helps to clarify what the 180 is and why someone would begin using this program.
Cheers!!