In short, because it is different Gospels. The Catholics on FR pushed me up that tree a long time ago.
We can and should do work on the “ground” level, but when one side says you are saved through Mary and the magistrum, and the other says you saved by faith, you have a mismatch.
See above.
"Whatever may be the future form of the relationship between our communities, we can, we must, and we will begin now the work required to remedy what we know to be wrong in that relationship. Such work requires trust and understanding, and trust and understanding require an assiduous attention to truth. We do not deny but clearly assert that there are disagreements between us. Misunderstandings, misrepresentations, and caricatures of one another, however, are not disagreements. These distortions must be cleared away if we are to search through our honest differences in a manner consistent with what we affirm and hope together on the basis of Gods Word."