Its because we are use to it. We all tend to avoid the area, but for 1st timers or those that come for a 2nd or 3rd visit, and make NYC their vacation for the year, for which the planned and planned for months, it means a lot. Really nothing compares around the world. Its typical for noob visitors to visit the cliche sights, while seasoned explorers will venture into the outer boroughs. But in the end, who cares if people love the place. Let them have fun.
Although one thing is annoying, and thats when they stop suddenly to take pictures in the middle of a busy sidewalk.
But people really do love this city. I remember seeing peoples eyes glow with new life looking out the window when landing at JFK. For some, this city is a dream come true to visit. Often, they leave in sadness. Not because they didn't enjoy themselves, but because they want the lifestyle.
And this is why NYC tourism is flourishing and why there has been such an effort to improve it. Because this city is addictive and if you increase the high, they keep coming back and they do.