Having multiple people on the lease is not a strange practice in Australia; it's normal and not as you described. When signing the lease you're not signing for a room, you're signing responsibility for the rent and condition of the whole house/unit (excluding responsibilities remaining with the landlord, e.g. maintenance). Each of your housemates are too.

Rents are expensive. It makes no financial sense to live by yourself.

Even in my home town - which has no substantial university - it's generally assumed that if you rent and do not have dependents, you almost certainly have housemates.