My operating hypothesis is this one: Chevy doesn't have a well-tested way to engage the physical brakes of the slightly weird dual system the Bolt has, and while 99.999% of the time, it would never even have to deal with those physical subsystems, it's still not ready. (Does anyone know if the friction brakes on a Bolt even have an automatable booster system, or is it just the ABS pump and muscle power?)Timing?
Different braking system?
Something held back for another model year upgrade?
No one knows except GM.