Because of our need, curiosity, fear etc, photographs of people or with people in them are probably universally intriguing to everyone. Historical photographs probably also fall into our curiosity of the past.

Landscapes usually have an appeal if it's not what we see every day in our own experience.

Unfortunately now with the bombardment of images we probably have become jaded to most pictures except the primal ones that deal with fear, sex, death, and maybe hope.