err, Djibouti port is even much closer to Addis, and they already have an electric rail and road connection, and yet Ethiopia is still looking for other routes.
the distance between Eritrea and Addis is 1,230km, the distance from Lamu to Addis is Around 1,400km, relatively speaking, that distance is negligible, Not to forget the border region between Eritrea and Ethiopia is so mountainous that non of the two countries dared to invade the other because they knew it was a logistical nightmare, there is a 600m steep climb in altitude, any infrastructure project to create a seamless connection will be more costly...
On the other hand, The $1B Addis Isiolo highway will be complete next year, The s.sudan kenya highway too is also under construction
And why are you comparing the economies of UG vs Tz???? in this argument, Tz is not in the same category as UG, compare TZ with Kenya because they both have access to the sea, Uganda is a transit destination, just like Rwanda..... For tz rail to get to Ug border, it will have to go through Rwanda, Burundi..... No one knows when that will happen, Tz keeps ground breaking and awarding tenders but as long as actual construction hasnt started yet, its all just paper castles, and dont also forget, to get to the Ugandan border is just the first step, Uganda then has to construct the rail from the border to the big cities...when and if that happens is unknown variable too.
Also, here is Ethiopia rail masterplan - you will notice both the rail link to Kenya is in phase two, the rail ling to Eritrea doesnt get to the border