I’m not sure that’s true for all forms of writing but I’d love to hear more about it.
Publishing a blog, for example, is pretty likely to be read by at least a small group of people. Same with a book. If I’m writing in a personal notebook, than no, it’s not likely to be read. On the whole, the statement is probably true, but for specific forms, I suspect it’s false.
Speaking from personal experience, writing something once increases the chance that future me will say something in direct conversation with at least one other person. So for me, there is a positive, non zero benefit.