Most cars use DOT brake fluid, which is hygroscopic. By absorbing moisture, it needs to be periodically changed, typically every 2 years. Thus, for example for a 20 year service life the brake fluid needs to be changed 9 times in its lifetime in addition to the initial brake system filling. On an internal combustion engine car this can be done when an oil change is performed, but electric cars lack oil changes and thus the brake fluid change is the only reason why you would like to bring the electric car in for service.
This requirement to change the brake fluid adds major maintenance costs to the owner of a car. Considering that manufacturing typically becomes less expensive over time but labor becomes more expensive over time, the need to change brake fluid can be a major obstacle for many to owning a car.
Bicycle component manufacturers have chosen a different kind of brake fluid. All Shimano hydraulic disc brakes use mineral oil as the brake fluid. It generally doesn't deteriorate. It is not hygroscopic so the moisture absorbing problem is not there. A once properly bled braking system typically lasts easily for 10 years or more with no bleeding or fluid changes required, provided that the bicycle is not routinely stored upside down, a problem which might affect some bicycles but no cars as nobody would ever park a car upside down.
Thus, there seems to be many advantages to using mineral oil as the brake fluid instead of DOT fluid. Car manufacturers however have not switched to mineral oil. Why is this the case? Is there some advantage of DOT brake fluid that I'm not seeing?
