Aside from making a city more popular, landmarks also improve the value of the buildings and structures around them. The value of the properties surrounding a landmark increases because of it. The real estate around the area appreciates even more. This is why properties around an important landmark are typically expensive, making their resale value also high.
Landmarks are the heart and soul of any place. Without it, a city would not be too interesting to visit. They may be ancient structures or modern buildings, or even statues, and they're there to impress, educate, and inspire. It is important for any city to take care of its own landmark so it can preserve its past so the future generations can still see it.