>>2010282Because it's safe.
The intrinsic safety of your typical Euro signalling system allows for 1 wrong-side failure per 100 million to a billion hours. The whole thing will by design have a tendency to suffer cascading right-side failures at the first default.
Another issue is that once you've repaired it, you need to run tests to make sure you've repaired it right. Every burnt cable is dozens of wires to test, and the way signal boxes are designed, there's a hard physical limit to how fast you can do that.
Safety is bad for availability.
