people who "dont get it" might be dumb
pretty self-explanatory story. like yeah i agree it's a bit confusing in the first 20-30 minutes, with the vague whispering and shots of the earth forming, but even then you can still kinda put the pieces together to understand what the meaning of it all is. but after that, once it gets into the kids growing up, there's no excuse for not getting it. it's incredibly straightforward and easy to follow if you're not an idiot, it's just told in a way that's not atypical for western filmmaking.
the same people who hate this probably love interstellar.