Macquarie's dropped in all major rankings - and very much so in the Beijing and THES rankings.
It's unclear why, really. If anything, the university seems to be improving. I mean I think the campus feels better than it did when I first started there in 2005.
To be frank, you should ignore rankings. I will give you an explicit example: I go to one of the best universities in the world, no-one can really dispute that. However, it's usually ranked below Harvard. But for what I want to do, Harvard is awful; there is only one full-time professor there in my field, the library isn't particularly good, they haven't got good fieldwork, my related fields (linguistics and archaeology) aren't particularly strong there, I don't think Boston would be a very nice city, etc etc etc.
You need to look at the university for you. Rankings are intrinsically irrelevant.