In fact, we're all to blame. Paparazzis are paid ridiculously huge amounts of money for such photos, because readers love magazines filled with such material. If people didn't buy tabloids, paparazzis wouldn't be paid so much for their job. A cruel job, by the way.
And here @ Bellazon, you can find so many candid pictures, many of them taken by paparazzis. Even if I'm against the whole concept of "spygraphing", I tolerate it silently, because posting candids is not forbidden on the forum. Maybe it should be..?