But the electric components are not standardized. You can buy e-systems from Bosch, Yamaha, Shimano, Fazua, Mahle, Stromer, Bafang et cetera and they all have different dimensions, different mounting holes, different communication protocols and different chargers. If you need a replacement part as a consumer, you have no choice but to buy the same part, which is usually quite costly because of lack of competition.

Not my experience here - I bought a Giant eBike which has a Yamaha powertrain... which is neither fish nor fowl. Battery is Giant, motor is Yamaha, but it uses a different comms protocol between motor and battery than the later Giant-only ones, so it's actually Yamaha... and notorious for comms failures. Battery says it's OK, and motor says it's OK, but there's a comms issue between them, so no power. I'll need to spend time sitting on a 1-wire serial comms link to have any idea what's wrong (rumour is that the transistor that powers this in the motor is a common failure point).

Some of these batteries can't be re-celled as if they've had a failure, the BMS deliberately goes into a 'permanently dead' mode, so it can't be recovered even if the dead cells are replaced.

It's criminal what's happening in the proprietary eBike space.