The ratio of 2 toilets for 162 passengers and 1 toilet for 12 passengers is very lopsided.
Then we have the carts. And emergencies. And queues down the back where it makes sense to refer passengers to front toilet close to descent.
I think some get precious about what they believe their rights are in flight. Some even think economy class passengers shouldn't be given champagne from the front in case they drink it dry and there's none left for business class passengers later.
If the business class toilet is unservicable can you use the toilet down the back and inconvenience econony class passengers?
Anyway when I book my economy seat I don't bother reading the entitlements of those sitting at the front. I'll use which ever toilet I feel is appropriate at the time based on crew direction. If you don't like it send Qantas some feedback along with priority luggage, priority boarding etc.