The reason they all fail is because of lack of content for end game BUT they fail in that way because they refuse to learn from the titans. Why do you think minecraft and terraria have had such a long healthy life. It's cause they have a robust modding community. They need to make the game around making it easy to mod for regular people. Look at minecraft skins, they're easy to make and sites have easy tools to help make em so everyone dips their toes into it and creates unique custom content to add to the minecraft skin library.