They're basically a big battery switch that disconnects when the car is parked or if a fault occurs.

However, in the fault case, pyro disconnects can be used (explosively cutting the wires). They're far cheaper.

For the 'parked' case, MOSFETs inside motor inverters have low enough leakage current that there isn't a need to power them down.

The only remaining time it's useful to have the contactors disconnected is when doing maintenance on the high voltage system (motors, AC compressor). That's a rare enough event that I would think the technician could just remove some bolts to physically disconnect a wire for maintenance.