Its a very much historical question. The time Ethiopia was under pressure of European force in Africa (England, Italy, France etc) the Ethiopian proclamation was drafted, which is still in power today, meaning we have to take the feeling and political situation of that time into consideration. In the today Ethiopia this basic understanding or feeling / non citizenship for non Ethiopia still exist!
Time has changed but the Ethiopian proclamation not, which is very clear if you where not born in Ethiopia you can not apply!
Of course we find still today quite a few people in Ethiopia, which were born in the country mostly through a relation ship of a non Ethiopian and a Ethiopian, as well we have still some families in the country going back 3 or 4 generation, such as Armeniens, Italiens, Greek etc......Some of these people have a Ethiopian citizenship. But in practice I do not know of people having dual citizenship, beside some pure Ethiopia Diasporas living in US or Canada.
oliver