The focus on Microsoft is odd. I remember most people using WordPerfect for DOS and other non-WYSIWYG word processors up until around 1993. These were much better for focusing on writing. MS Word came from behind and started to take over as Windows 3.1 and then Windows 95 became standard. Word wasn't the best word processor back then and was very buggy, but Microsoft succeeded in marketing it as a natural companion for Windows and bundling it with Excel and PowerPoint, and WordPerfect was slower to move to WYSIWYG.

The rise of the web was also happening at that time, and this article doesn't give it enough attention as a major influence on document format and a motivation behind markdown.