Moving a city is not as simple as saying "any time a building wears out, rebuild it 100/500/1000 miles away, repeat until finished." At the very least, there's logistical issues and economic disruption at both ends. It may be possible in theory, but, again, extremely challenging and unfathomably expensive. And humanity has a well-established track record with anything that involves committing vast amounts of money now to save a bunch of people, mostly strangers, in a few decades.