1) I don't see what is immutable about this logic. Next to the "people who enjoyed that also enjoyed..." list there could be a "to go a bit deeper..." or "books

1) I don't see what is immutable about this logic. Next to the "people who enjoyed that also enjoyed..." list there could be a "to go a bit deeper..." or "books referenced by this book or author..." 2) The problem is in "enough". People who will want to read about that book are only a niche and will never be more numerous than people who simply bought the part II and III of the Three Body Problem (it is a trilogy). The author here really points out an unaddressed problem. 3) Another argument to make a separate "book referenced by this book/author"