I’d suggest the accounting costs are the potential killer. Our small ACT plan (19 units) has our sinking fund of in the order of 10 of thousands in a couple of term deposits.
Tax rate will be max 30% company rate . I have wanted our plan to self prepare our tax return using the ATO short form strata return here
https://www.ato.gov.au/Forms/Strata-title-body-corporate-tax-return-and-instructions-2019/
I estimate it would take about 15 minutes to fill in the details and send it in. Unfortunately I cannot convince our committee to do this so we are left to pay the SM/accountant several hundred dollars to prepare a standard company tax return. So as said above, paying this, plus tax only leaves us a very small gain.
I would have thought that a large strata scheme with large sinking fund would definetly want to have it invested. And if the scheme was of a size to have other income (rental of common property spaces to commercial entities etc) or be of a size to be required to be GST registered and so needing to do periodic Business Activity Statements to ATO the accountant fees for annual returns may already be needed.