Because there are shows, museums, points of interest. You should try it sometime.
I like the Museum of Science and industry in Chicago but unfortunately some idiot built a city around it.
Many if not most people choose a vacation destination based upon climate, natural beauty and the opportunity to relax. Manhattan represents none of those things. I enjoy going there myself, but relaxing it’s not. Three to five days max and I’ve got to get out, I start to understand why people are so pushy and rude. Yes there are cultural attractions, shopping, restaurants and fascinating architecture. People watching without compare, from the lowest low to the heights of fashion. But, to me that’s a long weekend, not a vacation by any stretch.