I've been running it about 4 years now? It's very low maintenance (run process_new_comments.py every month and re-deploy). It also doesn't bring in much money: it's definitely a hobby rather than a business.
I don't do any marketing, most traffic comes from people mentioning it on reddit or from being included in "cool internet stuff" newsletters. I have some ideas for marketing, but I also hate marketing and do enough of it for my day job SaaS.
So I just run it because I really enjoy it! I used to have a newsletter but stopped that as it was too stressful having a regular deadline and dealing with email spam filters. Everything else about the site I enjoy: writing occasional blog posts, looking at culture through the lens of books, finding new books. I really like books: I used to own and run a bookstore, and a book price comparison website in the past.