i gotta be the devils advocate here
nearly every fairly large show does this, or something similiar
its about longevity, not peak
given that the majority of anime/manga fans watched in the first 3 days... sustainable viewershiprelies on new audiences
It's big achievement if you factor in that we are talking about Live action of animes which usually don't go so well.
It even surpassed Strangers in this regard.
And, definitely it's about longevity but you have to understand something here - when you get such massive peak like this then it fuels mouth to mouth publicity and other media outlets start covering it more - which means more viewership and more revenue.
Getting this peak is important for longevity.
Heck, I saw a video from my country covering LA with nearly 400K views talking about how good LA is...