Failures are much more dramatic than successes, and people like drama. I think this is why automobile races draw such crowds. People expect spectacular crashes, which we tend to find more interesting than cars just racing around the track. The same is true of bridges, buildings, or any structure or machine.
Typically, highway bridges have about 50 years. But over in England, they have iron bridges approaching 250 years. In France, there are Roman aqueducts that are approaching 2,000 years old. So a bridge can last a very long time if it's built properly in the first place and then maintained properly.
I was always told that I was good in mathematics, and I guess my grades and standardized test scores supported that. My worst subjects were those that generally involved a lot of reading - English and history. So, having good test scores in math and mediocre ones in reading, I was naturally advised to major in engineering in college.