French toilet habits

A rant.  Why do the French seem to delight in crapping in the bushes and among the picnic tables in their (very nice) Motorway Aires?  Nearly all of them have decent loos now (sit-ons as opposed to the old squatters) so why don't they use them?  The worst example we found was in the very pleasant small Aire on the road between Dreux and Evreux.  OK, so it's not motorway.  But the picnic area was covered in small heaps of bogroll and - how shall we put it? - ordure of the human variety.  What's wrong with the bloody loos?  They're open 24/7; they're free; they're even quite clean.  Is it the right of every Frenchman to crap where-ever he likes?