Making any piece of infrastructure natural disaster proof is a costly endeavor, and often not economically feasible, especially along long linear corridors. There are too many locations where a slide, washout, or overland flooding can occur that the owner is forced to prioritize and harden the highest risk locations. Risk is the product of likelihood of the hazard impacting the asset and the consequence of impact. Making an entire asset bullet proof would break the bank, but aiming for resiliency - focusing your money and effort on those highest risk locations and having an appropriate design intent (sometimes a less robust design that allows for outages is more economical that the Cadillac design, even in the long term).
All this being said, climate change and the impact of past human activities are making it more and more difficult to figure out what frequency and magnitude of event the owner should design for…the 500 year storm is becoming much more frequent in areas as are wildfires (and the following debris flows and floods) influenced by both climate change and heavy-handed fire suppression. So this is actually a fairly complicated topic…one the railways, DoTs and pipeline operators are all sorting through right now.