There are degrees of off/standby. It's good engineering practice and environmentally that when you "soft" power down, you turn off as many internal circuits as you are able and only retain basic functionality required to turn back on again.
Camera sensor off completely
WiFi chip in low power / periodic transmit mode
CPU at lower clock speed or sleep mode with periodic wake up timer.
Not doing this means that the camera designers were either:
1) Lazy and unprofessional
2) Planning to retain the camera functionality for nefarious uses.