I think part of the reason could be : Like most of the German Army the majority fought on the Eastern Front, At least in theory each SS Pz Division was supposed to have a a Werfer Abt. organic to the division.(1,2,3,5,9,10,&12 reported)
At least Two Wefer Regt. (83&84) were reportedly in Normandy in July 1944. And for the Bulge one book gives 8 werfer brigades reported.
[sources German Rocket Launchers in WWII Schiffer & Field Rocket Equipment Almark Publications Sources like poster are getting dated check other source before taking as Gospel!]
Bill
#:-)