Does "the historical circumstances of our federal constitution, and the difficulty of amending it" really explain it? Australia also has a federal system, and Australia's federal constitution is also notoriously difficult to amend.

I suspect the biggest factor is actually the Bill of Rights and the 14th Amendment-once courts get used to the power to strike down legislation on the grounds of constitutionally protected rights, judges begin to feel the temptation to interpret those rights in such a way as to fulfil their own policy preferences; once those so tempted get their way, inevitable debate ensues about the propriety of their having done so.

By contrast, Australia's constitution is rather light on protections of individual rights, which limits the ability of Australian judges to feel the same temptation-one feels much more secure in striking down a law as violating the 1st Amendment, than striking down a law as violating the "implied right of political communication" (Australia's equivalent-which, as the name suggests, is not explicitly in the text, only having been read into it by the Courts, and only extends to "political" matters).

So, I think that explains how originalism became much more politically coded in the US than in Australia. However, I think the fact that it got coded as "right-wing" rather than "left-wing" may be an accident of historical circumstance. Hypothetically, suppose the Lochner era didn't end in 1937, and for decades thereafter SCOTUS continued to strike down labour regulations as violating the constitutional right to due process - one could imagine in such a scenario how originalism might become appealing to many people on the political left, whereas those on the political right might have been comparatively disinterested in it. In such an alternative timeline, "originalism" might have ended up being coded the opposite way.