Blind people still have bodies and other sensory perceptions to relate visual meaning to. Temple Grandin is a high functioning autist who describes how visual thinkers translate words into pictures, because they think pictorially. LLMs don't have any embodied, grounded contact with the world, so their only understanding can be statistical/symbolic pattern matching of text. Which isn't how language works for humans, since we use words for our experiences as social animals moving about and manipulating the world with our bodies.