page A has content about apples. page B has content about bubblegum. Canonical tag states that page B should refer to page A. What is the point of that? all link juice, all ranking potential is passed to page A, even though page B has very different content. So page A MIGHT appear in search results about bubblegum, but page B will not because it is passing all link juice and rank potential to page A about apples. People stop going to page A when looking for bubblegum because it is irrelevant, and bounce rates increase.

Dont think you need documentation to get this. If you have all pages redirecting bots via canonical urls to the SAME page, it is pointless. If you have several article about apples and point them all to page A that is a different story.