I am surprised that no one has pointed out the real reason.
In Australia the Government banned the public from owning military cartridges so 303 MkV1 and MkV11 was out. So as Australia still have factories to produce the Lee Enfield cartridges like the 303x54R ( this was made by puling the barrel and turnign off one turn of the thread and deepening the extractor slot), 25/303, 270/303 etc came about. Add the costs and import duties added to help "pay" for the recent war.
Plus of course there was loads of Lee Enfields available cheap. In the UK firms like BSA, Parker-Hale, London Armoury, Greeners, Stirlng were building fine sporting rifles on the Lee Enfields and the P-14/17's however in the UK we had restrictive laws and of course Stalking was not for the common man.
Australia and Canada plus the African colonies had far more scope for the budding nimrod that the home country. India was already highly restricted in to what sporting arms could be used and 303 British was a very big No-No. The government there even today does not trust it's populace with firearms. The restrictions in the UK are minor to those in India even today. Across the boarder in Pakistan it's easier to own a firearm but hunting is all together another ball game.