USB is host processor controlled. In ordr to be sure that communications take place within the time slots required for successful handshaking the host computer must have lots of power or it will mist the slot that it needs.

Most other communications do not require this for example Ethernet where the control for the comms is inherent in the protocol and the host computer does not need to concern itself with it.

You may never have problems with USB but a lot of people will and it is not a good thing to rely on.