Money is part of how we move through the world, what stores and restaurants we go into, whether we take a train to the airport or a taxi. Describing characters living in the real world requires describing them engaging with money. There are also so many emotional aspects to money - feelings of inadequacy, feelings of security. I am not sure if there needs to be more about money in fiction, but the absence of this aspect can make a story feel somehow frictionless and unreal.