The UK was incredibly reliant on the Commonwealth for all sorts of resources - the Germans wanted to cut them off and it was a lot easier to find the merchantmen near their origins or destinations than it was in open ocean. So there were German commerce raiders operating off the coast of Australia in both World Wars.
The Japanese were a growing concern but this was still just a little before Pearl Harbour and the start of the war with Japan.
Ummmm... you need to review your history. The Germans had colonies in Africa and in the Pacific. The Germans fought in the Pacific in WW1 and WW2, and there were of course numerous global merchant raiding missions conducted by the Germans on Allied shipping. The only reason the Japanese didn’t do that is because they didn’t have the fuel and their navy was more optimized for shorter ranged missions involving heavy combat.
https://en.wikipedia.org/wiki/German_colonial_empire
Drachinifel video on the circumstances of HMAS Sydney’s last fight against the German merchant raider Komoran:
https://www.youtube.com/watch?v=_cObwTdbeAY