I think you're talking about the pay-per-click model. Most of that is offered at such a low rate. It's a penny per click kind of thing, so if you have written a story or you've written a chapter of a book, you'll get a penny for every person who reads it. That could take a long time. That means a hundred people have to read it for you to make a dollar, so to do a transactional payment like that is very problematic.
On May 31st, 2018. See this statement in context.