User retention has several important factors:
1. Marketing
2. Development
3. Design
These points are almost exclusively all for whoever develops the website. The problem with StoriesSpace is that it has a very dated design, and I think it's highly probable that the developer responsible is busy elsewhere. They need to reach out to users via newsletters, social media, and more. They need to update the design to bring it in line with modern standards. The system also needs polishing as some things are very clunky. This is why users are using more accessible, better functioning, better looking, and user-friendly websites like shortstories101.com though it's probably a smaller community, it's still growing and has active ongoing development.