They do.Back a long, long, long time ago, in a land far, far away...when I was a hospital orderly, I administered quite a few saline enemas when patients got constipated (it seems like everyone gets constipated in the hospital)
It's a combination of a lack of exercise, an abrupt change in diet, and that many illnesses and diseases involve dehydration. These thing--acting together--cause this issue (among other things).