The difference lies in the sensitivity to the changes in the system. If we slightly change the bridge (e.g. the width of one beam by a couple of percents) the properties won’t change much. If we change one of the building blocks of a superconductor we’ll probably get a material with a very different properties.
The difference also lies in the used equations to predict the properties of a system. For a bridge we need classical mechanics, where the equations can be solved in a relatively short time, while for a superconductor the Schödinger equations need to be solved, which can take a huge amount of time.