It's a lot easier to isolate your atoms from noise. There's a giant nuclear fireball blasting half the planet at a time with EM, everything is radiating EM (ev

It's a lot easier to isolate your atoms from noise. There's a giant nuclear fireball blasting half the planet at a time with EM, everything is radiating EM (even on some of the communication bands!), most of the things will diffract or reflect EM, and we don't know of a way to isolate EM using only EM. So atoms seem to have a better asymptotic isolation in known physics, and thus conceivably might always be faster due to potential noise in the respective channels.