Highest grade Australian from what I read is not comparable to Japanese one

You can, for example, find A5-equivalent beef raised in the US. The thing is that ranchers found that Americans in general don't actually like wagyu very much. Honestly, everyone I know who's had it did it for the novelty, and never again. My favorite description is that someone once told me it was "like eating a candle", and I can't disagree that much.

That said, there's a much larger market that deeply enjoys more traditional beef that's been bred with Japanese cattle to become extra marbled. So that's what ranchers grow, in general.

I assume the same is true in Australia. High-grade wagyu, like some many luxury foods, is an acquired taste.