This is because understanding is an intrinsically personal experience. To convey it to others is to choose words, phrasing, and sentences which best express what is in one's mind.

Call it "intention", call it "understanding", call it "effective communication." The lack thereof is obvious and easily identified.

> Most success stories of LLM coding are ports. Because someone already did most of the job with the original code, sometime even twice if we count the tests.

Another way to phrase this is:

  Because someone already thought about the problem and what 
  needs to exist in order to solve it.