In my view there was no need to extend the SGR to kisumu and Uganda. Naivasha is a central place where everyone from western, kitale, turkana, kisii, migori, maralal etc can collect their cargo.
Also the SGR was being built to serve kenyans not ugandans so no need to tax wanjiku to extend rail to uganda border. The british built the rail to kampala because at the time their interest was uganda, the pearl of africa, and not kenya.