Passenger trains are relatively light and well suited to battery power, compared to freight rail. Particularly for short and medium haul. It really doesn't seem like a difficult technical challenge--it can be done with existing technology. Probably there is no market for it yet, which is why they haven't really taken off yet (much like hydrogen trains).
The market is there, it's the full-service proof of the technology that's lacking. We are only starting to see ready-for-the-road prototypes.
They are coming, I'm sure, but we are still a bit short of readiness to accept orders.