@Joram , In most of the 'developing world', cables are laid in much the same way as in Kenya, dig a hole, put your cable,cover it up and let your competitor or the guy doing the road come and redig and re-cover to put a similar cable.
In the developed world(I struggle to think of an example at the moment), an organisation say the City Council or even an infrastructure provider such as KDN digs and builds concrete conduits that look like the sewer you are talking about and anyone who wants to do an underground cable has to pay to use the space. So you don't have all providers digging to lay their own cables. Faster,cheaper and more aesthetically pleasing!
An easier solution for Kenya et al would be overhead cables like the power lines. I don't know why no one seems to prefer this option. Maybe it has some inherent disadvantage that we are unaware of.
On a lighter note, I've heard stories of fibers being cut because the last time there was a fiber cut, the guys who repaired it gave me a tip for helping them find the cut. So every time I get broke, I cut the cable and help those guys fix it! Peasant farmer ingenuity at its best.