Distance, travel times, communication, and cultural differences were the practical barriers. The Tubingen Lutherans did reach out the the Orthodox (after Luther’s death). There was some dialogue on the Lutheran Augsburg Confession, but the Ecumenical Patriarch was preoccupied in local politics and didn’t want to get involved with 'schizmatic Rome’s issues. Dialogue came to a general standstill. It ended with the Patriarch essentially agreeing with the Lutherans on some things, but asking questions about others (he was especially concerned about the Flioque and the number of sacraments - Lutherans did not number them and left it too open-ended for him). He told them not to talk to contact him about theological things again, but only to write as a friend.
Modern talks have been more fruitful.
The thing to keep in mind is that the Orthodox way of understanding ‘theosis’ is not entirely congruent with the ‘justification’ model that grew up in the West. Rome and Wittenberg ‘evolved’ one way, the East another. Lutheranism exists somewhere in the gray area between the two, but its closest sibling in common theological terms and thinking is Catholicism. (Well, probably some bits of Anglicanism and then Catholicsm… but you get what I mean.)