Don't know what the story is, but I can see in the case of the WW2 sets that
WG would be uninterested in carrying them in favor of their own products. Those sets seem to be currently available via Mark Mondragon and DreamForge Games:
http://dreamforge-games.com/collections/all but I don't know if that's just burning off the existing stock or if he's taking on the lines
WG have seemingly dropped.