This may also be a contributor to the fact that a lot of devs these days seem to make a clear distinction between the type of code they allow themselves to write and code they won't write. A lot of people stay within a narrow range of what their chosen framework allows and don't really experiment with doing complex stuff themselves. In my view someone who has worked with React or Node (example) for a while should have a fairly good idea how they are imlemented but it seems many people accept it as "magic" and don't look behind the scenes.

To me reading source of these frameworks helps realizing that whoever developed them are just human beings like the rest of us and write regular code that's really not special.