Why is New York City replete with scaffolding?

New York City is my favorite collection of ironies. The city is renowned for its culture and sophistication, , but locals think Breakfast at Tiffany's is an invitation. Despite the world's largest subway system, traffic perpetually clogs Manhattan's streets. New York is also known for its stunning architecture, but hideous mountains of scaffolding obscure every other building. Even though natives and transplants get used to seeing the city blanketed by these oppressive eyesores after a few years, the obvious question remains unanswered. Why is New York City littered with scaffolding? 

Well, first of all, it isn't actually scaffolding. The structures are known as sidewalk sheds, and they're surprisingly helpful. In the video linked above, the YouTube channel Half as Interesting explains why New York introduced the sidewalk sheds and why getting rid of them might be impossible.