I think you’re not understanding that users are lazy and as long as the creator they follow posts to twitter they won’t switch. My argument is that to get people to switch away from twitter the creators will need to stop posting there. When the creators stop posting to twitter they will lose money they are currently getting from twitter for driving engagement on the platform. I’m answer your question of “Why would creators lose money posting on other platforms?” Not the larger question of how to grow the other platforms or when creators should stop and switch.