Why are Star Trek fans so emotionally invested in the concept of "canon"?

A few weeks ago on Facebook, I jokingly asked whether Virgil's Aeneid was "canon" for the Homeric Epic Universe. I got some funny responses, but the most insightful answer was that the concept [ADDED: of canon as it applies to fictional works rather than religious texts] just doesn't apply outside of a capitalist context. Without the idea that someone "owns" the stories and controls how people use them, "canon" is whatever a later creative work decides to take up as part of the world it's building. Hence Homer is canon for Virgil, and both are canon with Dante -- who also throws in the Bible, which definitely would not have been canon for either Homer or Virgil. The mixture might be unexpected, but what matters is not whether the Homeric epics and the Bible are "really" in the same "fictional universe," but whether the thing that Dante creates by combining those "canons" is good. (Spoiler alert: it is.)

I'm not here to question what materials are "canon" for Star Trek, but instead to ask why we all seem to care so much about a distinction that is ultimately based on a faceless corporation's control over the intellectual property of Star Trek -- especially given that neither corporate entity (CBS or Paramount) has exactly covered itself in glory in the last decade or so.

One thing that's weird about this investment in "canon" is that there are a lot of times that people seem to give "beta canon" material more de facto authority than actual episodes. VOY "Threshold" is widely regarded as nonsense, despite being undisputed canon, while people routinely refer to the backstory to the reboot films that appeared in non-canonical comic books. More often, though, people are dismissive of beta canon material, based on a widespread misconception that Daystrom is for in-universe theories based on canonical materials only. Yes, few of the novels are literary classics, but I have read novels that are better than almost any canonical episode. So it's not a matter of sheer quality.

I personally regard Christopher Bennett's Department of Temporal Investigations novels as absolutely authoritative for the interpretation of Trek time travel, even though he would never presume to include them in the official canon. Closer to home, I also view the "Borg farming theory," developed by a number of Daystrom contributors, to be the authoritative explanation for the Borg's behavior. I don't view them as authoritative because some corporate entity told me they're "real" Trek, but because the explanations they offer are elegant and more thought out than anything we ever see on screen. Nor do I claim that everyone should accept them as the basis for their own thinking -- only that I would tend to keep them in mind when launching my own theories.

Coming from the other direction: a lot of people go to great lengths to develop theories that effectively write Enterprise out of the Prime Timeline. Why not just openly say that you don't care about Enterprise and don't regard is as "real" Trek? Coming at it from the perspective of the faceless corporations, why did the reboot films have to create a confusing time-travel scenario to verify that the timelines forked? Why not just say that they are writing new stories about Kirk and Spock that don't treat the old episodes and films as canon? Marvel seems to have managed to make a bunch of movies without explaining their relationship to the old comic books and no one was terribly confused. Presumably they knew that Star Trek fans would be obsessed about their canonical status -- but again, why?

What do you think, Daystromites? If you are deeply invested in the canon concept, can you explain why? If you are not, do you have any sense of what others find so crucial about it?

ADDED: A lot of people have commented that canon guarantees plot continuity, but that's not necessarily the case. It's possible to have continuity without having canonical status -- the "relaunch" novels and Star Trek Online are both in continuity with canon material (though not with each other), and presumably have continuity within themselves too. And you can have canon without continuity -- half the posts on this board testify to the fact that Star Trek canon is full of contradictions. In fact, maintaining an ever-expanding canon increases the likelihood of contradictions, simply because the new writers are only human and are bound to make mistakes or forget things. So canon is a separate concept from continuity, hence you can't defend your love of canon simply by pointing to continuity.