Well yeah, everyone does, and I choose to buy into it.
No one is saying you have to.
Paradoxically, "canon" is both the most AND least important aspect of a franchise. For some people it's vitally important, and shapes their enjoyment of it because they use it to decide what is "truth" (and ultimately whether they like the franchise and the directions it's taking). For others it's irrelevant - if the "Aliens Holiday Special" is Officially 100% Totally True Canon Forever according to Fox, it doesn't actually matter because no one is
forcing them to accept it. It's a multimedia fiction franchise meant for entertainment, you should take from it what
you want to, not what someone else (corporate, fan, or otherwise) tells you to.
I've known people who disliked what happened to the Alien series when 'Aliens' came out, so they only considered the first movie to be "canon". More power to them! If that's what makes them happy, then thumbs up.