They aren't replaced, for instance Saga of Slime and Devil got a new chapter after I spent some time working on other stories. I personally lack the motivation to work on one story at a time, and I fluctuate between them. If I didn't have these other stories, it would just be a few months of uploads then a few months of nothing. The only one I've abandoned is World's Finest Mage because I lost interest in the World's Finest Assassin series