Of course, not everyone travels for this reason. There will always, and perhaps increasingly, be a place for travelling to places with all the familiarity and comforts of home.
But seeing the evidence of history that has shaped nations is one of the unique aspects of travel. It's also a big draw for tourism. Just take a look at Prague, Paris, or even fast-developing Beijing, and the number of visitors they attract.
Although it costs a lot to preserve cultural heritage, it's too late once the historic attractions are gone. That's why plans to "modernise" Hong Kong's Stanley markets, the new Bird Street, and knocking down the Great Wall of China to make way for roads can be detrimental to a country's wealth in the long run.