Notice that boxing generally became popular in English-speaking areas in the world during the latter part of the 19th Century. In regards to Australia, give credit to Jem Mace and especially to Larry Foley for making that commonwealth an incredible hotbed for boxing activity and the incubator for an astounding amount of top professional boxers at that time. Keep in mind Australia had a population of less four million people during that period. Foley is one individual who richly deserves to be inducted into the International Boxing Hall of Fame for his massive contributions to the sport of boxing in general, the development of many top boxers based in Australia and the establishment of Australia as a boxing hotbed during the early days of boxing under the Marquess of Queensberry Rules. - Chuck Johnston
Jem Mace and Larry Foley certainly, yes. It's worth noting that in the second half of the 19th century the authorities in England made serious efforts to prosecute prizefighters and organizers of prizefights. Moral crusaders and a zealous new breed of police and prosecutors existed in Victorian England, and blood sports and boxing had been under a sustained attack for several decades. Australia was a far more welcoming environment, full of wide open barren spaces, rough characters, mining communities brought there through the gold rushes, and sons of convicts made good. Even to this day, or in very recent years at least, the culture of tent boxing has continued in Australia.
What Unforgiven said. Simple answer is that it was legal. The U.S. and Great Britain had too many laws banning or limiting boxing. Australia mostly allowed boxing to have free reign, so it flourished at that time.
The Australian era tends to get a bit overlooked these days. For a very brief period, Australia might just have been the foremost boxing nation.