I suspect it's a matter of context: one or both agents forget that they're supposed to be delegating. ChatGPT's "memory" system for example is a workaround, but even then it loses track of details in long chats.
When I read a book, for example, I do not keep all of it in my short-term working memory, but I also don't entirely forget what I read at the beginning by the time I get to the end: it's something in between. More layered forms of memory would probably allow us to return to smaller context windows.
And then in terms of reading a book, a model's training could be updated with the book, right?