Why does Australia tend to censor games A LOT despite a copy having a foreign classification rating?

I know about certain titles getting banned outright (Halloween, Hotline Miami 2) while some are released in the country with a form of censorship (such as the casino being forbidden to interact in GTA V, the corpses disappear in Left 4 Dead, etc.). even though those games have been classified abroad as there are other bodies for classification: CERO (JP), ESRB (US) or PEGI (EU) to list a few examples from other countries.

They’re all separate from rating movies (while apparently in Australia, they use the same rating system for movies in games) hence why they tend to get either banned outright or censored. Even if you import a copy from abroad into Australia, isn’t the existing classification enough? (Like if it’s rated M17 in the US, its roughly equivalent to a R18+ or if it has CERO C (15+) from Japan, similar to either a M or MA15+ rating).

Couldn’t an Australian gamer just be like, if they possessed a “banned” title in AU but has an foreign copy of that game with an existing classification from its country of origin, isn’t that already enough? It has a rating but not by the Australian Classification Board (rather its foreign counterpart specifically for games). Just argue that a M17 (ESRB) rating is closest to either a MA15+ or R18+. Same with CERO D (17+) or CERO Z (18+).