I don't think it is fair to blame the fans as if they were the ones who invented this notion of canon and them applied it to the franchise. This invention belongs to the TPTB.
Not really. "TPTB" generally don't have to worry about the question of canon, because what they create is automatically
canon. That's simply what the word means. Historically, it's only been fans who have had any reason to worry about the question of what stories were and weren't part of the canon. Originally, of course, canon was a religious term referring to the writings that were officially approved by the church as the genuine word of God, as opposed to the apocrypha, alternate texts that don't mesh with the church-approved ones. Apparently it was Sherlock Holmes fans who first applied the term to distinguishing the core writings of Arthur Conan Doyle from Holmes pastiches (i.e. fanfic) by other authors.
The idea that canon is something imposed by "TPTB" dates back to Roddenberry's 1989 memo where he tried to define what was and wasn't counted as part of Star Trek
canon as he saw it, including the omission of the animated series from the list. That created the perception among fans that canon was something specifically dictated by the creators and defined by what it excluded. But contrary to what fans have assumed for the past couple of decades, that memo didn't represent standard operating procedure for all creators. Heck, Roddenberry's successors didn't even continue to honor the memo after he died. There's also been Lucasfilm's attempt to define formal "levels of canon" for Star Wars
tie-ins, but of course those so-called "canonical" books have been freely ignored and contradicted by actual new canon, because it was erroneous for Lucasfilm to use the word "canon" that way in the first place. Canon simply means the core work by the original creators, or their inheritors. Anything parallel or supplemental done by other creators, any tie-in running alongside the main work, is not part of the canon. That's not a value judgment, not a condemnation, merely an acknowledgment of distinct categories and their distinct natures.