The question is how we write,not why we write.Probably it has something to with the process.I look at writing as the process of forming and re-forming ideas because it is while writing that a majority of the ideas begin to form ,evolve and grow into bigger ideas and thought movements. The logical process within takes a concrete shape while words are being formed .This can be evident from a stopping in -between while words are forming when suddenly you realise that you have reached a point which was far away from your starting point.You begin to realise that you have reached certain recesses of your thinking which you never thought had existed in your mind.