The cost of automating the entire fleet itself AND every station. These trains are designed for incredibly long lifespans and a lot of the fleet is still relatively young.

The old silver sets wouldn’t be able to be automated (they’re all mechanical), Tangaras are running a computer from the 80s, and the new trains are expected to have another 20 years and are under a SLA for everything.

It’s not so much about the complexity of automating a train but the complexity of doing that to an entire network as well so as the cost and time. You’ll be shutting down swathes of network for years at a time (Epping-Chatswood, Bankstown) for upgrades which would include having to provide alternative transport, the installation of the relevant hardware on every station, and hiring a plethora of station staff after culling them.

Cars are a little more isolated and don’t have huge investments in infrastructure (and the vehicle itself).

It will happen eventually but I can see it taking more than 20 years. Just because something may be technically feasible doesn’t mean it’s economically feasible.