There are as many answers to this question as there are readers. The best sounding answer is that we read to enlighten our world, to learn and to experience from other viewpoints. Sometimes we read simply for entertainment. I love a good murder mystery but I am not trying to learn how to get away with murder, or how to solve murders. I simply want to enjoy the story.
For me, another reason to read, a not very highbrow reason to read, is to calm my mind. Sometimes I enjoy reading after very stressful or busy days. The order of letters lined up creating words, the order of words lined up creating sentences, and the order of sentences lined up to create ideas causes a very calming effect, ordering my mind. If random letters can be lined up in ways that make words and sentences, and these sentences can illuminate grand or maybe even mundane ideas, then my mind and my spirit can do the same. In the same way that straightening a desk or a room can calm me, reading the words on a page can calm the mind. Of course the best part is that these words generate ideas and dreams, the result of which is my ordered mind begins to dream, to run, to take off and fly to non-orderly but wonderful places. I reap the benefit of order and calmness, followed by creativity and dreams. I might even learn something along the way!