I think landscapes do very well with the general public and beginning collectors because it's easy to understand, pleasing to look at, and ultimately easy to live with. When someone buys a print, a print that could cost hundreds or thousands of dollars, they are often making a commitment to live with that image in plain sight for a very long time. Some people may feel uncomfortable having the continuous gaze, of people they do not know, "watching" them around their homes. Landscapes don't intrude and they can take you to a place of beauty or adventure. Personally the only photos of people I want hanging on my walls are those of people I know.
More experienced collectors might already have boxes full of landscapes and seek more unusual or provocative images. Then again a well done landscape, or one that is more unique, can still find a home with a seasoned collector. As for 90 percent of the photography collectors being in NYC, I'd have to disagree with that. Certainly there are many collectors there, however there are many collectors all over the US and other countries.