It probably has something to do with the fact that Ethiopia is fairly inhospitable, and fertile grounds and places for civilizations were found elsewhere. Not too hard to understand IMO.
Not sure that is the reason Tyler, You may find this link of interest.
History of Ethiopia - Wikipedia, the free encyclopedia
I can tell you why but you may not believe me...
I've witnessed that ethiopians are EXTREMELY apathetic. They have that "I don't care" attitude. They are rather carry 10L of water 5-10km every day than buy say a bicycle and use it for that....or put money together and dig a well.
In restaurants waiters did not care about tips and were very bad.
Hotel owners had the same attitude. You'd come in for a breakfast and they would not have anything except juice and some bread. You'd tell them you can pay anything they ask and they would still not do it.
I shared my thoughts with my guide and he said that it's a huge problem for the country as it's a big issue here.
Nobody cares to do more than they absolutely have to.
So, they can improve their living conditions,but they just don't care enough to do it. Of course, that's a generalization,but it's what I observed.