would guess its all about money. Kook sponsor mostly australians , 2/3 aussies have a Kookaburra. and have never been ones for top english sponsorship really.
I dont think kookaburra were every really big in the uk they are more poular in Aus because they have Ponting Hussey,Haddin endorsing them they are some of the biggest and best in Aus cricket while in the Uk they have 3 eng internations that have been in and out of the team Shah ,Wright Ambrose and formerly Yardy and Morgan
The UK would definitely be a great dumping ground for volume sales of Kookaburras. They have the best of both worlds as they buy in US$ and sell in GBP and AUS$.