Because languages are not the codes we use to organize communicative intentions. Communicative codes are previous to language. If interpretation fails, it's not because codes fail. Codes are inherently lose, inherently interpretive, inherently inferential, and inference is by definition a lose procedure, just as the cognitive ooze contains lose intentions which result in utterances and other things. The codes I'm talking about, communicative codes, transduce intentions into utterances, and then utterances into interpretations.
Codes are previous to and relatively independent from languages and from other signaling systems.
Codes mobilize signaling materials from languages, kinesic and proxemic systems, and probably from other systems we are still unaware of. More precisely, codes transduce communicative intentions into sets of multimedia signals, and then other codes translate these sets of signals into inferential interpretations of intent. In each of the interactants, these mental states are first cooked into notional or semantic representations . These semantic representations include referential and propositional contents, beliefs, values, dispositions, affect, shared knowledge, etc. And here is where communicative codes emerge, as organizing devices to make sense of this cognitive ooze.