I agree it is historical rather than theological.
Remember, Protestants protested against the Catholic Church, not the Orthodox ones. The Orthodox ones had broken off way, way before the Protestant Revolt (er, Reformation ). The Orthodox had no problem with the theology, it was the primacy of the Roman Bishop (i.e., the Pope) that got their knickers in a bunch.
So, I think it is just remnants of ill-feelings.
Theologically speaking, all of the things Protestants dislike about Catholicism are true in the Orthodox Churches: Bishops with Apostolic Succession, dogma, reverence for Mary, Seven Sacraments, only males in the priesthood, etc.
So, I think there really is no reason except long-lasting bad feelings.