Intuition at GR-scale problems. Why I need to believe in Einstein postulates if I can just look at walking droplet 2D model of QM and see that these postulates are obvious?
Why do you need to consider Einstein's postulates if you can just look at a ball traversing a rubber sheet with a depression in it, for that matter? Same answer: because these rough analogues are not background-independent -- you would see a very different picture in each case if you moved the walking droplet or rubber sheet setups to the moon or to the ISS.
Einstein GR postulate number one: microscopic physics is background-independent.
These experiments' microscopic details behave the same on Earth, on the moon, and in the ISS, but their macroscopic behaviours sure don't. You have to input details of the local structure of spacetime into each of them if you want to predict their results (e.g., what trajectory the walk takes, or how long it takes for a ball to reach the bottom of a depression in the rubber sheet) successfully.
