As far as I know he was going through a very difficult phase of his life, having lost his son and separation from his wife. Some people from the Sri Aurobindo Society approached him during that time to record some bhajans for the Divine Mother and he agreed. If you notice by then or soon thereafter he switched from ghazals to bhajans. There may be more to it but I am not aware of it.
Affectionately,
Alok Da