Uh? Then how do I plug my USB-C Samsung phone into an USB 2.0 A port on my laptop with an official Samsung cable found in the phone's box? Do I misunderstand something? Is the cable "illegal"?
The real reason is to prevent hooking up two dumb Type-A host side power supplies, as I pointed out in another post. A properly implemented Type-C device will not draw high currents without power negotiation. (I'm looking at you, Nintendo)
Cable not adapter. IIRC a cable is okay but the adapter version is not. Like mentioned above/below, this is to prevent other USB-A things from causing problems. When you have a fixed cable, you remove a lot of the potential issues for misuse.
Any adapter that has a USB-C receptacle is prohibited by the standard. This limitation exists to prevent hooking up two USB-A hosts with a USB-C cable.
