What does Ghost offer that can't be accomplished on Medium?
Which is a huge deal for some people (myself included). I don't really trust other services to remain around, especially when doing so might put my content at risk. I'd much rather be in control of where my content's hosted, even if it means I need do some of the more fidly management and setup things.
Using Node, while something the developers probably liked, might not have been the best decision because it severely hinders adoption by the casual users that WP currently owns.