Most rabbis do not allow conversion for ulterior motives (e.g to marry a Jew), because it is not for the sake of God.
Let us look at the words of the prototypal convert in the Tanach. What did she say?
And Ruth said, Do not entreat me to leave you, or to keep from following you; for wherever you go, I will go; and where you lodge, I will lodge; your people shall be my people, and your God my God; Where you die, will I die, and there will I be buried; the Lord do so to me, and more also, if even death parts me from you. (Ruth 1:16-17)
Does she talk about her love of God, of Israel, of Judaism, of monotheism, or such? No. She talks only about her love of Naomi. So why was she accepted and held up as an example?