I don't think it's that bridges need to be able to withstand that much heat, but that no one should ever be able to apply that much heat to it. If a pipeline runs under it and is able to be accessed by anyone, that inherently means the infrastructure is strongly vulnerable to attack and it just takes one person mere seconds to destroy everything.
I'm not blaming the designers of the freeway though. My house has a giant plate glass window right next to my deadlocked front door. Our entire society is built around trusting that most people don't want to destroy the nice things we've collectively built. But if someone smashed my window and stole my TV, I'd probably make sure that window was a little more secure. Incremental improvements.
At least you aren't being stupid and weighing the window/door risks backwards leading to installing a double-keyed knob or deadbolt. That's the insanity that happens from poor risk analysis.
I'm not blaming the designers of the freeway though. My house has a giant plate glass window right next to my deadlocked front door. Our entire society is built around trusting that most people don't want to destroy the nice things we've collectively built. But if someone smashed my window and stole my TV, I'd probably make sure that window was a little more secure. Incremental improvements.