Maybe because it wasn't built by the Chinese. But it doesn't seem like a complicated project.
I deal with contractors. Where whenver you see sub standard work and corner cutting, most likely the man has been squeezed for everything by some rent seeker and is trying to make ends meet. He would cut on most essentials.
Most of the public structures are built with half of what is required. That appears to be a structural weakness. That points at weak of few steel or weak cement/ concrete. Where the structural engineer recommended a much bigger steal bar, the contractor bought a cheaper and slightly smaller. They are so clever it takes a keen engineer to tell the difference.
I also learned that the thing that can never be hurried is the construction of a bridge. Time is part of the construction process. Casting of cement must be done at the right time and allowed to cure. Uhuru must have rushed to get it launched in time for Jubilee campaigns. We may see more of that on the SGR