Sounds like botched distribution engineering to me
A site like this will have a high voltage distribution network, operating at 11kV, perhaps with a backbone at higher voltage, e.g. 66kV. In order to provide redundancy, much of the network will be interconnected so that it is possible to switch off any single part such as a breaker, substation or cable for maintenance without affecting users. A major consideration in such networks is fault level. This is the current that will flow into a short circuit until a fuse or breaker interrupts it. Obviously the fuse or breaker has to be rated to interrupt the fault current, which may be in the mega amp range, otherwise you get the kind of failure described here.
What is sometimes not obvious is that the more interconnected the network is, the harder it is to estimate the fault level accurately, and the easier it is to exceed equipment fault interruption ratings by having all the links closed. High fault capacity switchgear is expensive, and will generally not be installed at the lower levels of the network. I suspect that for the reasons stated by others, tight cost control, poor project management and security paranoia have combined to produce an unmagageable distribution network.
The intersection of two major power corridors probably complicates the whole issue as well.
There is a procedure called "Phasing Out" to counter precicely this problem. Even so, equipment should be rated to interrupt fault current without damage to non-wearing parts.
Once an ionised path has been established, 11kV goes exactly where it wants and will chew up EVERYTHING.