It seems like a very modern phenomenon though of online fan theories putting creators in a bind.
I remember a long time ago seeing this fan theory for LOST that was done as a comic, it was like really well done and detailed, people get pretty nuts about this stuff.
Now why creators pay attention to fan theories and don't just come up with the story they want to tell beforehand is beyond me.
Money, dear boy.... Slapping on an unecessary addendum to a finished story and/or pandering to the loudest, most supportive contingent of the fandom are good ways to extend the run of the gravy train. Making and selling a hot property is every creator's dream, as most will never know wild levels of success (and many creators are lucky if they can even make a living doing what they love most.) Who cares about the integrity of a story or the destruction of its legacy when there are second houses to buy and kids to send to college? Just hop on board the USS Sellout and ride that ship to the end of the line! Give the fans what they want! And when they scream in outrage because what they wanted was terrible, just block them on social media and call them small minded if they disagree with your creative decisions.