It is only wasted if you accept their valuation and don't keep the vehicle. Insurance companies allow you to buy back your totaled vehicle, which can then be resold as-is, parted out, or used as a donor parts vehicle when shopping for the same make and model.

Yeah, but if it's an actual write-off because the frame is structurally unsound, there's really no way to get that sunk value back. (And storing an extra vehicle for parts is really... not practical for the vast majority of people.)