I think the biggest mistake here is that we expect the Orthodox to think like Catholics. Western legalism needs to define something in the absolute, yes and no. So the Western Church sought to define who has valid orders and valid Sacraments and have declared the Apostolic Churches (Eastern Orthodox, Oriental Orthodox, Assyrian Church of the East) having valid Sacraments and a valid priesthood.
In the East there is a level of comfort in accepting that we do not know something. So they know that they possess the Orthodox faith, therefore their Sacraments are valid. They are not sure if the Catholics have valid Sacraments and thus would not risk profaning the Eucharist by giving it to someone who may not be baptized validly. Of course there are also Orthodox who think the Catholic Church is outright heretic.