@tim99 - Unions
Trains on the London Victoria tube line have also been automated since the line opened. The meatsack at the front just opens & closes the doors and presses "Go": A job the platform staff could easily do via a remote.
If you look at some of the safety systems on trains (speed limiters, obeying signals, being awake, etc) they're just there to ensure the meatsack does what it's supposed to do (The electronic dog). So why not just remove the meatsack? As others have mentioned, trains are so big and heavy that they couldn't stop in seconds if the meatsack saw an obstruction on the line.
The main reason driver automation hasn't been done (In the UK at least) is the trade unions.