Bridge builders mostly don't have to design for adversarial attacks.

And the ones who do focus on portability and speed of redeployment, rather than armor - it's cheaper and faster to throw down another temporary bridge than to build something bombproof.

https://en.wikipedia.org/wiki/Armoured_vehicle-launched_brid...

This is exactly the problem. You can't build bridges if the threat model is thousands of attacks every second in thousands of different ways you can't even fully predict yet.