If I were to speculate, and say it's probably because (1) they might not be interacting directly, and saying "(possibly indirectly) interacting" is a lot more s

If I were to speculate, and say it's probably because (1) they might not be interacting directly, and saying "(possibly indirectly) interacting" is a lot more syllables than "talking"; and (2) "talk"/"communicate" emphasizes the information-theoretic content, whereas "interact" is somewhat more likely to be interpreted in terms of interaction strength. (If two systems are "barely communicating", they are transferring a small number of bits, whereas if two systems are "barely interacting", the influence in displacement/impulse/temp/whatever is small.)