Well, there seems to have been enough demand to support any number of companies outside the UK. Aldis was diversified into other fields, so they could well have afforded to keep a hand in the scope game. Of course, seeing the obscene prices the gunmakers wanted for ex-WD scopes that they doubtless got for trifles probably put off quite a few potential buyers before WWII.
Ex-WWI scopes must have been plentiful enough in Europe too, but Zeiss certainly sold a lot of new scopes in the 20s and 30s, especially in the USA.
Anyway, I think we all know the story of industrial decline and the reasons for it in some countries. I see China has just passed Germanyas the No1 exporting nation in the world. Not bad for a country of 82 million, eh? "Germanophile I ain't, but them's the facts."