Constipation Causes Bed-wetting

There was a study in 2012 that concluded that constipation may be the reason for Bed Wetting.
There are endless forums and authorities that says that the first line of action for constipation is increasing the water intake.
What caused the FDA not to withdraw the drugs which resulted in deaths of children in 1993. That too after FDA said that it is aware of the deaths and is actively monitoring the situation.
What is more disturbing is the fact that author of the study did not pursue the matter further – why they did not pursue the study further?
In case of children who drink more then adequate amount of water and other fluids and are suffering from constipation, there is easy cure. Add a pinch of salt for 2-3 days and restore the perfect health to all the children.
Even salt medicines could be made to regulate the amount of salt that can be given to children to cure them of constipation.
Why there are medicines in the market to cure constipation?? When it is well known that medicines have serious side effects.
The above questions are serious enough to cause distrust among government agencies and public.