Due to the way the text of a comment becomes an increasingly light shade of grey the more that comment is voted down, it seems an odd choice to display the text of a post such as this one in grey as opposed to black. It always takes me a moment to remember that I'm not necessarily viewing an unpopular post.
It’s to discourage text posts.
They’d rather you posted it to Medium or your blog or something, and then post a link to that here.