Why do Australians prefer plain easy English over rich English?

The other answers are good, but I like to step back with questions like these, to the cultural context.

In former times, expertise and professional use of language were elite activities; people who would use language professionally had an education that encompassed the literary canon and rhetoric; and the dominant literary aesthetic prioritised an extensive, nuanced vocabulary and shows of erudition.

Currently the literary aesthetic has changed, to something more sparse and less preoccupied with nuance and flourish. Professional use of language has been decoupled from literature and erudition. And Plain English has been elevated as a priority in that professional use of language, particularly given the amount of information professionals are expected to digest daily. People write in dot points, not in paragraphs. People write for other people who would rather not be reading your stuff at all, and certainly don’t look to be entertained by it.

That’s not just in Australia. That is throughout the Anglosphere.

It does not extend to the entire world, though. In particular, it does not extend to the Subcontinent (if I can surmise correctly from OP’s name), at least not in the education system. Babu English may be a nasty colonialist term, but it does continue to reflect a disconnect in values around language aesthetics and utilitarianism, between the subcontinent and the rest of the Anglosphere. There is a concern about using rich vocabulary and structure, which other countries have simply abandoned in their education systems, in favour of efficiency and clarity.

I’m trying to avoid value judgements here. Some things were lost in the transition, other things were gained. I am certainly not proud of point form becoming my native discourse. And in fact, I have used words here that have made me feature in Masiello’s Mega Words.

But I don’t use those words in my day job. And I don’t expect to read them there either.

OP is certainly right about one thing. This is indeed a cultural difference.