NHTSA has been historically reluctant to reduce EVERY standard it has ever had on the books. A classic example is the parking brake requirement. In an automatic transmission vehicle, the parking brake is redundant to the mechanical interlock in the transmission. You can’t even turn the engine off, unless the parking pawl is engaged. Yet, the NHTSA regulations not only require a redundant parking brake, it also must use a “friction element”. Modern electronically controlled transmissions and braking - stability control systems make this totally unnecessary.
I don’t believe NHTSA will ever give up this type of control, unless congress actually passes a law requiring it.
The parking brake can be used when parking on a hill to relieve the transmission lock of undue pressure. That makes it so much easier to move the lever from “park” to a motion setting.