While that may be obvious to you, it's not obvious to a lot of programmers (myself included) who grew up learning about object orientation, abstractions and modelling behaviour on the real world. ECS's for all their added complexity come with the breath of fresh air that is classical imperative programming where all the data is just available.
There are scant few sources for learning this, Handmade Hero being a notable exception.
There is CS literature about component oriented programming.
That's not at all what ECS's are about.