Because its the Mecca and cultural hub of the universe. Ive been to over 30 different countries and there is still no city that compares to NYC. Just get someone who knows there way around. And im not even a big city person. I like my space. but you gotta see it
There are individual exhibits at individual museums that are worth the trip. Just offhand, the Egyptology exhibits at the Met and at the Brooklyn Museum are both almost as good as you'll see in Egypt but you can have a beer after.