Some people just don't snap that many frames. Some people pick up a camera, and then decide that it isn't really their thing. And also some people make bold face lies about shutter counts. 20k magically becomes 2k, and if it is actually noticed in time to matter it is easy enough to laugh it off as a typo and 'apologize' for their foolish mistake.
Depending on your shooting style it can take a VERY long time to rack up all that many frames. I mostly do sports photography, which and churn out several hundred an hour, or wildlife shots where I can come back with a hundred or two frames from an afternoon. Then I can turn around and do landscapes or something, where I'll go out for a weekend and come home with six frames, three of which were me bumping the shutter button as I was getting the camera ready.
Canon EOS 7D | EF 28 f/1.8 | EF 85 f/1.8 | EF 70-200 f/4L | EF-S 17-55 | Sigma 150-500
Flickr: Real-Luckless