Why, Mark is very popular among her base of fans and supporters? Better than a impersonal press-release.
Because this gave zero notice to millions of people who were interested in her decision. When so many are interested, it's traditional some notice when an announcement will be made. Now folks will hear the news from every imaginable source, in every imaginable way. Many won't believe it at first.
Bad manners, and I don't buy any nonsense that it's unique and wonderful and anything special. Just bad manners.