When I was a child, a professional writer told me that you should only write for the love of writing, because you can't expect to make money with it. It stuck with me. I've been lucky to make a little money in recent years, but my reason for writing remains the same: it's a labor of love. I don't see that going away.
Some writers do like rewriting. I'm one of them. And it's lucky, because I've had to do a LOT of rewriting.
I don't know about the decline of readership, but I do not believe the world will ever run out of stories. Every new era, every new historical and cultural development — hell, every new person on the planet — will bring new stories into being. For people who love fiction (and not everyone does, and that's fine), it's a source of knowledge and solace, an education in how the world works, a proof that we're not totally alone, an escapist outlet, a release valve — any of those things and more. When I discover a new book I love, that book instantly becomes irreplaceable for me.
Sure, I also feel that way about favorite movies and TV shows, but sometimes I want words; sometimes I want visuals. They're distinct media offering distinct types of storytelling experience; they can co-exist.
Have you read New Grub Street by George Gissing? Anyone who's really interested in knowing whether making a living as a writer is tougher now than in the past needs to read this novel, published in 1891. It's about two ill-fated writing careers and one successful one, and the author is unbelievably dark and cynical about his chosen profession. This is a book where the decision to quit one's day job and write can lead to divorce, bankruptcy, and death. There's a lot of writerly self-pity in it, but also some great insights — for instance, we learn that even in the Victorian era, catering to aspiring writers was typically more lucrative than selling one's own fiction. Many things change, yet it's both sobering and oddly encouraging to learn that the core of writerly angst is not new.