Why do people post photos in which they walk? Playing with their animals? Dinner? Why write about anything at all? It's a common way of expressing yourself. A person talks about his daily life to other people, shares something, but this does not necessarily carry the goal of standing out or "showing off" by the fact that he is very hardworking and does day and night. Surely he wants to think that someone is interested in it, that someone cares. But I will not generalize, because some people really just like to collect praise and attract attention in this way.
Perhaps people want to draw attention to their extraordinary person and how hard they "work" in the name of the greatest goal. Sometimes all these goals are conditioned only by material desires. In fact, they would like to exhibit photos of their asses with even more dumb subscripts, but not all are rich in natural physiological data.