Because they copy paste the gameplay, in different environments. Like “travelling to the past”. I recall AC being praised for the accurate portrayal of the environments they presented. Idk if that has persisted.
I have never played the game and never will because playing a game where your dude gets into a machine to watch the memories of an antecesor of you who was a kick ass assassin and then playing as the assassin doesn’t really call me, but it did to plenty people.