> I think my question at this point is what about this is specific to LLMs. Humans should not be forced to wade through reams of garbage output either.

Beware I'm a complete AI layman. All this is from background reading of popular articles. It may well be wrong. It's definitely out of date.

It has to do with how the attention heads work. The attention heads (the idea originated from the "Attention is all you need" paper, arguably the single most important AI paper to date), direct the LLM to work on the most relevant parts of the conversation. If you want a human analogue, it's your attention heads that are tacking the interesting points in a conversation.

The original attention heads output a relevance score for every pair of words in the context window. Thus in "Time flies like an arrow", it's the attention heads that spot the word "Time" is very relevant to "arrow", but not "flies". The implication of this is an attention head does O(N*N) work. It does not scale well to large context windows.

Nonetheless, you see claims of "large" context windows the LLMs marketing. (Large is in quotes, because even a 1M context window begins to feel very cramped in a write / test / fix loop.) But a 1M context-window would require a attention head requiring a 1 trillion element matrix. That isn't feasible. The industry even has a name for the size of the window they give in their marketing: the Effective Context Window. Internally they have another metric that measures the real amount of compute they throw at attention: the Physical Context Window. The bridge between the two is some proprietary magic that discards tokens in the context window that are likely to be irrelevant. In my experience, that bridge is pretty good at doing that, where "pretty good" is up to human standards.

But eventually (actually quickly in my experience), you fill up even the marketed size of the context window because it is remembering every word said, in the order they were said. If it reads code it's written to debug it, it appears twice in the context window. All compiler and test output also ends up there. Once the context window fills up they take drastic action, because it like letting malloc fail. Even reporting a malloc failure is hard because it usually needs more malloc to do the reporting. Anthropic calls it compacting. It throws away 90% of your tokens. It turns your helpful LLM into a goldfish with dementia. It is nowhere near as good as human is at remembering what happened. Not even close.