But for example if they used PMM squirrel cage motors etc, they would be nice and smooth, cheaper to build, more energy efficient.

On the battery front, using car-style or truck-style EV battery modules would be more robust and would reduce cost by somewhere in the order of 50%.

Instead, most trains still use induction motors (this is the high pitch whine you hear) and many train battery designs use industrial style rack mount batteries, with screw terminals, controlled by a massive PLC cabinet. In eMobility the controls are handled by a small safety-rated microcontroller.