No, wait, also, well said about the reason for rehashing the story: for all the little kids watching who never saw the first movie or the Kanto episodes leading up to it.
And even then, that's somewhat of a confusing thing in itself. Why remaster and re-air the first film and TV Special if you're going to assume none of the kids are going to/have seen it anyway? They even had the first film available for free viewing on Nico Nico Douga the day before the prologue special aired. How do these writers rationalize the things they do? If they had the kids in mind, why risk confusing the children that did catch those recent rebroadcasts?
For roughly the same reason that the prologue (as Silktree previously mentioned) was simply used to get kids into the theater seats; they think the kids be too excited to see the cool Pokémon do cool stuff to question the plot holes.