The last time I needed to catch public transport in Melbourne (excluding skybus) was about 2 years ago, the last time Mrs harvyk caught public transport in Melbourne was 7 years ago, little Miss harvyk has never caught public transport in Melbourne before. It's hardly a common thing for us to be doing, so why should we be forced to pay extra, for a card which we will use extremely rarely (if at all), just so we can pay our fares? It is highly unlikely that any of us will be catching public transport in Melbourne in the near (or even somewhat far) future.
Besides, it's not just Melbourne, I'm pretty sure I've seen some Sydney buses which are cashless as well. So what is a traveller meant to do, keep a collection of cards for each city they may intend on travelling to on the off chance they will want to use that cities public transport options?