Why is AI generated language so hard to understand?

A study found that AI-generated text uses psycholinguistic features that correlate with human processing difficulty more often than human writing or round-trip translation paraphrases. Nine frontier and near-frontier models used more inanimate subjects with animate verbs, more low-frequency n-grams, longer dependencies, more stacked nouns, and more reduced object relatives in conversation. The research suggests AI-generated text is increasingly optimized for goals like math, code, and reasoning rather than successful communication, leading to higher information density.