I think the main reason why Word is losing mindshare, is because it was designed for paper. The whole formatting system makes the assumption that there's a fixed width and height into which your text and images fit. In reality, a phone screen is a lot narrower and a widescreen monitor a lot wider.
Markdown never made these assumptions. For the most part simply because plain text reflows to fill whatever space you give it. But there's no way to position an image either, I imagine mostly for simplicity's sake. It can look goofy at times, but it never looks broken.
That's why I can write this comment on my phone and someone else can look at it on desktop and it's perfectly readable in both scenarios.