The reason is, among these fleshy physical organs, the organs of the antaH-karaNaM sit like a person in a chair; the chair is never identified with the person in that seat!
The heart also, when it is semi-physical, is the chair for the ego, as I told you earlier.
But we do not call some one with a lot of ego as one with a heart.
It is in the subtle form of the heart that love, unlike anything else, penetrates deep into the core, and that is why we identify love with the heart.
Further when we refer to Bhagavan as *hRdaya-vAsI* we are not saying that it is He who sits in the semi-physical heart donning the robe of JIva with an ego.
We are actually saying that it is He who shines forth from inside having melted the physical into the subtle by Love at its peak of excellence.
Maybe we are not understanding it in all this detail but at least we understand that He manifests himself in Bhakti that is full of Love.