What you have explained is very true, but the fact is Uganda railway net work is very very unpredictable up to now, the section from Kampala to Malaba is the one which at least for now is under discussion, remember Museven is not comfortable to take a loan from China because of the conditions that direct Uganda to use the same construction company and all other rules and regulations that govern construction of Kenyan SGR, first is expensive per KM, second Uganda needs electrical while Kenyan is diesel, Museven wants to use competitive biding like Tanzania.
But even if Uganda manages to build from Malaba to Uganda, the next profitable route is Kampala to Juba, because of the trade volume between Uganda and South Sudan, if you compare with Uganda to Rwanda, but this route is not likely to be constructed in the near future because of the following reasons;
1)Uganda economy can't afford to take another loan after that of Malaba -Kampala
2)Volume of trade between Uganda and South Sudan is not enough to make this route profitable, good roads are enough for the next 20 years
3)Security in South Sudan is not good to allow this capital intensive project
4)South Sudan is not in position, financially and security wise to pay and implement this project at the moment, they have more important projects to start with, like roads, water, health, electricity and security