No one is claiming the fans "know it all". But Reigns is just terrible on the mic and not good enough in the ring to be where he is. Even Don Cena had to win the US Title a couple of times and get his character over before he won the title (and he WAS over at that point, and deserved it).
Reigns has done nothing to deserve being where he is and isn't good enough to justify just getting it handed to him. It's basically because he's big and because he's related to The Rock.