I think the main reason people like using lightweight markup languages is because they don't have to depend on any special tools. I can comfortably edit markdown in any text editor, whether I'm using VS Code on my laptop, Notepad on a public library PC, Vim on a remote server, a form in my source host's web interface, or whatever it is that people use to edit text on phones. And I don't need to worry about the status of someone's proprietary hobby project.