Same reason markup/markdown is better for docs than Microsoft Word. WYSIWYG development just sucks. It's not diffable nor mergeable. Quick setup is simple, but

Same reason markup/markdown is better for docs than Microsoft Word. WYSIWYG development just sucks. It's not diffable nor mergeable. Quick setup is simple, but complex refactorings are plain impossible. Also there's always at least this one thing the editor fights you on.