Not everyone is used to that type of story, whereas you might have read or seen things like it a dozen times before. You have to feel sorry for them....
Time travel stories are a good example - a lot of us will have watched Doctor Who, read time travel novels and comics, and seen dozens of paradoxes explored. But some people will watch Bill & Ted's Bogus Journey and get confused. I've never understood people who said that the end of Tim Burton's Planet of the Apes didn't make sense - Tim Roth's character was left alive, and after Wahlberg went back he followed him back through the anomaly, maybe taking an army of apes with him, and thanks to the vaguaries of the anomaly, ending up back on Earth before Wahlberg even got there. But for some people the idea that one got back before the other doesn't make sense, even though they're both travelling in time.
To use a really funny example of how people not used to certain ideas can get things really mixed up, there was a review that used to run in the Radio Times of Highlander, which described it as a confusing time travel film - they had thought that all the flashbacks were trips back in time.
