They make a lot of money from the photos so while the general public buy the magazines there will still be a demand for the photos.
There are plenty of celebrities that actively court the paparazzi by phoning them and tipping them off as to what they will be doing that day and where!
Some celebrities who actually want a private life manage it quite well! You don't see many photos of Claire Danes and the like unless they are at an actual event or doing a charity promotion!