[mhays]

Cities don't tear things down, developers do. Generally.

A parking garage can be hideous and still make money. Most owners aren't going to tear down $10,000,000 in value so they can spend $30,000,000 and end up with a $40,000,000 building. They'd rather tear down $1,000,000 in value and make the extra $9,000,000.

An art deco skyscraper might be decrepit and below code. Getting it up to code and to where it's marketable might not be worth the cost/risk/profit equation. Once property taxes, insurance, maintenance, etc., are considered, it's easy for a building to be worth less in place than the land would be worth as a blank slate.

No easy answers here. Unless your city can draw high rents, in which case the math might (might) change to the positive.