इदं तावत् this one, ईश्वरस्य कृते for (fear of) God, यथाकामम् this act, कृतम् done, रामस्य Rama's, परित्यागे in abandonment, हेतुम् reason, न उपलक्षये I do not see.
'Or he might have thought he is the overlord and can do as he likes. (Or, he might have done this for fear of God) Otherwise, I do not see any reason for the abandonment of Rama'.