There's always room for a tool that does most of the things that people need to do, alongside far more complicated tools that do that plus a whole lot more. If all you want to do is maybe make some text bold or italic or have a bullet list, you can do it in Word, but it's way more than you need (plus it's not text), Markdown solves your problem, and if someone doesn't have a tool for viewing Markdown, it's still perfectly readable in a text editor.