This is a fundamental misunderstanding of what modern generative linguistics is all about (to be fair, it is extremely widespread). The aim of this branch of science is expressly not to "learn to produce and interpret varied utterances" (called E-language in the jargon), but to understand the cognitive processes behind the production and interpretation of utterances (called I-language). Now you may agree or disagree with the methods and assumptions used in the pursuit of this goal, but it is patently unfair to accuse the field of failing to do something it never set out to do.