No matter how hard the best dubbers and localizers try, translating an anime as perfectly as possible simply can't be done. It's because of this harsh reality that dubbers have no choice but to add new contexts or material to the original subbed anime. This isn't always a bad thing, and can lead to cool new details made exclusively for the dub.
Source：https://www.cbr.com/anime-dub-details-not-in-sub/
