This article omits an important aspect of popular SSGs and the 'Jamstack': they are not easy-to-install or easy to use by non-technical users.
Some of the most popular SSGs are surprisingly complex despite claims to the contrary. (A simple contact form is impossible in many SSGs without embedding third-party services.)
Also, the love of Markdown is not shared by anyone who isn't a developer. Step outside of basic Markdown and it becomes unpleasant to use and cumbersome. It's even harder for non-technical users - try adding a table using Markdown.
Outside of developer circles, SSGs have had neglible impact on non-technical users.