I don't buy into this argument, but it could be argued the patients had a liveable routine down before McMurphy came and disrupted their peace. Although none of them were actually happy on the ward with the Nurse, they managed to seek solace through the bonds they made with each other by taking part in little hobbies, such as poker, that got them through each day.
Since the Nurse needed her control, she made the men as dependent on her as possible, and, therefore, they could never be considered cured or get released. Most of the men were aware of this, and although some would deny it, they were happy about it because returning to the unstructured real world was most of the patients' greatest fear. In other words, they were living peacefully in their comfort zone until McMurphy came and disrupted it.