mostly because people do not mention it and often people who are from other countries, even from France are not aware that they should hold a certificat but as you can probably read from the DRAAF website it covers any form of looking after animals.
this does not mean you cannot ask a neighbour to look after your cat or dog or a friend etc but if you take someone into your home such as a pet sitter its then required so a bit of a grey area.
The other thing you have to look at too is does your home insurance cover you for house sitters as they are still classed as tenants as they are given accommodation for work.
Was trying to find the story of the German family who had a fire and insurance would not pay out here in France because the house sitter had no insurance. (i believe gites need something similar)
All in all its a nightmare to get your head around.