There are so many things wrong with this plan it's difficult to know where to start.
1) Building Code of Australia
* you have to have a certain number of non-habitable rooms (ie living rooms, dining rooms, etc - rooms without beds in them that aren't kitchens or bathrooms) for each habitable room (bedroom)
* each bedroom has to have a certain number of square metres per intended occupant
* there need to be a certain number of toilets and showers per intended occupant
2) Local council regulations
* as per what others have said, you can usually only lease to a single household, and if somebody else is going to organise lots of sub-tenants, they're not going to want to pay top dollar to the landlord - THEY will want to be the one to profit from it, not the landlord
* the head tenant, if they decide to sub-let, takes on all the same responsibilities as a landlord has when they let, so they'd run into all the same obstacles outlined in any case
* if you want more than one lease in place, you require special zoning, or permission for a "special use" in residential zoning, and you're extremely unlikely to obtain it
3) State government
* fire regulations - as others have said, the level of fire regulations imposed once you get above a certain number of tenants becomes quite onerous
4) Deciding "to heck with the regulations, I'll do it illegally"
* insurance will be invalid
* mortgage can be called in at any time due to lack of insurance coverage
* can and hopefully would be prosecuted, and hopefully would be sent to jail (certainly a possibility with regards to willing and fragrant breaches of fire regulations, as would be the case with the outlined scenario - fire safety is taken extremely seriously)
* leases would be unenforcable, so if tenants decide not to pay you, or trash your property, there's sod all that you can do about it, no recourse to landlord insurance
Is that enough to deter you?