An invisible rasengan catching a Kaguya level Byakugan user off guard?
:|
Plot and character nerfing. If the villain was really that powerful then it'd send all of the villages into another war...and Kishi can't finish that in a two hour or less movie.
Explain how Sakura was able to hit and damage Kaguya, then you will answer your own question.
The more appropriate question would be how Kaguya didn't see Sakura coming. :| Kaguya could have been too distracted by Nardo and Sauce.
She was really scared of those seals after all