When something happens to them, it's the tribal instinct. This gives an opportunity for people to feel connected to a famous person. The statistics and numbers don't mean as much until you put a face on it. Politicians are aware of publicity. And while Michael's visit hasn't translated into specific money yet, it was a tremendous help.
Politicians are people, and they tend to be more interested when celebrities speak out.
The attention of the press and public is brought into greater focus. And there are those voters who are now motivated and focused. And that will get attention. Politicians have two jobs, to serve the public interest and to stay in office. And nothing does both those jobs better than fighting sickness while shaking hands with stars.