That makes no sense!
The original jap copy was barely 6 Gigs.
My guess is that they upscale the videos and forgot to add any compression at all...
But the original videos already had great quality, I doubt it is any different now.
I honestly hate that trend.
I remember one KaguraGame translated game made in unity where the original jap version was 2 Gb and the translation was 6GB.
The game was exactly the same, they just forgot to enable the 'compress' files option when compiling the english build.