Earlier quoted context omitted.
My immediate instinct was to agree with you whole-heartedly. Then I remembered that Copilot has an "Explain this" button that I never click. Maybe this is because I'm just not used to it, maybe the workflow isn't good enough, or maybe it's because I don't trust the model enough to summarize things correctly. I do agree that this is an area that could use improvement and I see a lot of utility there.
This is great feature, but targeted mostly at junior developers who don't yet understand how particular library or framework work. But when I read the code, I spend most of my effort trying to understand what did original developer meant by this, and LLMs are not yet very helpful in that regard.
Even if I can reason about each line individually, sometimes code is just complicated and maintains invariants that are never specified anywhere. Some of that can come down to "what were the constraints at the time and what did we agree on", but sometimes it's just complicated even if it doesn't have to be. The latter is something I would love for a LLM to simplify, but I just don't trust it to do that consistently correct.