It should not be that expensive, but replacing brake fluid periodically is good practice, it is very hygroscopic and will cause corrosion and eventually seals will fail. But i3 brake fluid change should cost no more or less than any other car with that many disc brakes.

Brake fluid absorbs moisture from the air and it's boiling poing reduces over time, making it more likley that heavy braking will boil the fluid and kill the brakes.

I get that it needs replacing but owning several ICE cars, I can’t remember having a break fluid change on the very first periodic maintenance of the vehicle.

BWT, you use breaks a lot less on an EV, does that have an effect on degredation or is it simply a function of time?

But that's based on time not mileage.

No, it's based on people (understandably) not ranking car maintenance high on the list of things they worry about in the dark hours of the morning. So it's easier to just look at the odo, rather than ask the customer who is just going to (knowingly or otherwise) lie to you anyway.