Well, drive somewhere and get out of the car and the first thing might notice is the landscape (or cityscape, or cloudscape or seascape .... you get the idea). Some people collect what they like, and most people appreciate these things. A collection of street shots of say New York might not do well in a gallery out west, but then a collection of landscapes of the west might not do well back east.
Let's face it, the general public might prefer color work over black and white...recall a gallery owner in Santa Fe telling me that they needed a good platinum printer to include with the rest of the work...Why?..they felt it would appeal to some of the customers. Don't know that it changed anything, just something the owner thought would help move some of the work.
Even though I like landscapes, most of the work I do seems to be more urban in nature, because that is what is close by for me to work with. Learned my love of photography reading Life magazine...not many landscapes were featured in it..but a lot of good street, war and other photography.
If someone can actually figure out what the 'collectors' want before they do, they could stock up on it cheap and sell it for unreal prices.....but my crystal ball must be old and a bit blurry...because I don't have a clue. And since the feeling I get from most on this site is they shoot for themselves, not for what someone might want...it really does not matter.