Time Travel in Sequels

SPOILERS for Terminator, Harry Potter and the Prisoner of Azkaban, and Harry Potter and the Cursed Child ahead.
  1. What is it about sequels of time travel stores that they don't seem to understand the mechanics of their own predecessor?
  2. For instance, in the greatest time travel movie of all time...
  3. Duh
  4. The first film pretty clearly implies that time travel can't change anything.
  5. The machines failed not so much because the humans outsmarted them...
  6. But because they already had failed *in their own past*.
  7. Sending a terminator back in time caused the humans to send back Reese.
  8. And Reese subsequently fathered the leader of the uprising against the machines.
  9. It happened in our present time because it happened in the history of the future. It was inevitable.
  10. The machines either didn't understand this or, as implied by Terminator 2, they knew events unfolded for their own creation as well.
  11. There is only one timeline in Terminator. *The* timeline.
  12. All time travel accomplishes is moving consciousness/awareness of a few individuals around the timeline in a non-linear way.
  13. This is the only kind of time travel that really makes sense if you pick away at it.
  14. But Terminator 2 then tossed this out and rewrote the timeline entirely, setting the stage for the rest of the series, which gets consistently less sensible as a result.
  15. There's another time travel story I quite like...
  16. Duh
  17. Which has the same theory of time travel Terminator gave us.
  18. It is abundantly clear in hindsight that throughout the third act Harry and Hermione didn't actually *change* anything.
  19. They played their part in bringing about events as they had already happened.
  20. From their perspective the timeline is complicated. But consistent. Only one timeline.
  21. Buckbeak never died.
  22. The dementors were always repelled by Harry.
  23. Sirius was always saved.
  24. Future Hermione always threw stones to alert past trio.
  25. Etc...
  26. The joy of the story is seeing how this timeline unfolds from two perspectives and realizing it all fits together.
  27. But Cursed Child aborts this logic.
  28. In the case of Terminator it has been assumed that when Cameron gave up rights to the story, the people who took over just didn't understand his time travel visions and got it wrong.
  29. I always assumed Rowling thought long and hard about time travel and settled on the PoA model intentionally.
    Bonus that it's the model I like best from a story-telling perspective and the only model that doesn't get hopelessly inconsistent and paradoxical.
  30. But I have no explanation for how Cursed Child switched theories of time travel.
  31. ¯\_(ツ)_/¯