I think a _part_ of the problem is due to being confined to the dimensions of your screen. If I'm reading code in one file which relies on context from another file, I can bring them up side by side in my editor, but the value in doing that diminishes with the more files / context I need in order to understand something.

Sometimes I wish I could project my IDE onto the wall behind my monitors. Programming in VR would probably achieve the same thing, but I'm not ready to move into that world yet.