It makes more sense in the context of Australian culture. Gallipoli as a military campaign is presented as our first campaign as a federation (federated in 1901, individual colonies contributed soldiers before then), and as a "coming of age." And part of "coming of age" for an adolescent is rejecting their parents in some way. The movie has fictional characters based on the work of the historian Charles Bean, who was all about "Aussie larrikins and gallant soldiers being betrayed by British stupidity."
There are all sorts of myths about it. For example, that they were all good Aussie country boys - most were urban, and 30-40% were born overseas. The number is uncertain because for example some Aboriginals signed up, which legally they couldn't, so they got written in as being from Vanuatu or something. But at least 25% were born in the UK - the film, along with the various other tellings, absolutely never presents a common soldier of the ANZACs with a British accent, at best there might be a rebellious Irishman who hates the English like poison.
In Australia we tend to have three accents, not regional but social. There's a nasal one we'd call "ocker", a general one probably 80% of people have, and a faux-English accent associated with higher educations. To American or British ears all three accents would sound about the same, to Australian ears the educated Aussie sounds English. This was used to deliberate effect in the film, to perpetuate the myth that "we landed on the wrong beach" and that British officers were indifferent to casualties, and so on.
The Gallipoli campaign was also the brainchild of Churchill, then Lord of the Admiralty, and in WWII Churchill as PM basically abandoned Australia to the Japanese once Singapore fell - to his mind, the main war was in Europe, Asia could wait. It's notable that the US once it came in concurred in this view, but still there's a sense of betrayal, "our boys were fucking about in North Africa while the Japs were coming," etc. Aussie historians are wont to portray Churchill as an incompetent idiot, and again Aussies as gallant larrikins, blah blah.
And there's the fact that the ANZACs weren't exactly alone there, but there were British, French and Indian soldiers, all of whom vastly outnumbered the ANZAC force. But according to Australian history Gallipoli was invaded by 6 Aussies and their donkey.
And so on and so forth. There's a lot of context to it, so that Aussies will get the message even if foreigners don't.
It's the usual self-serving nonsense most countries engage in. And to take it back to roleplaying, well every group has the guy who keeps fucking up but blames everyone else...