Please elaborate, what data are you using for your assertion.
If am not mistaken, Tshs 30,000 (Kshs 1,500) in Tanzania can get you to Kigoma from Dar, a distance of more than 1,000km.
In Nairobi, we have a commuter train that travels a distance of about 20km, and the last time I checked, the fare was 40Kshs (Tshs 400)
In my humble opinion, the wear and tear involved when running a fleet of buses within the city surpasses a commuter train that carries 1,000 passengers at a go.