I think building software is more like building a whole city for millions of people in one go. The bridge has a very simple goal, to cross from one place to another. Also you would need to speed up time a lot for it to be comparable. Imagine if technological change was so fast that by the time you finished building the bridge there were flying cars everywhere.

Blueprints are not that important when you need to build something that needs to adapt. Take for example olimpic stadiums that no one uses, they might have good blueprints and all the regulations but who cares now they are still useless. On the other hand take the exampole of haussman buildings in paris they are still being used and proved very adaptable.

I guess it might have something to do with nassim taleb's concept of antifragility. Software is very rapidly proved to be fragile because it operates in a context where there are a lot of black swans. On the contrary bridges operate on another time scale wher it might not be so obvious how fragile they are but given the correct scale you would have bridge builders facing the same problems as software developers.

[edit] Also you need to take into account the crazy fact that you build software based on some facts but the software you build changes those facts, so now you need to change the software that will change the facts so on and so forth.