> This sounds dumb but it just simply is much harder to keep context about what's going on around if you can't refer back to it because it's on the same screen or one short mouse scroll above or below your current screen.

To note, a common effect of not DRYing functions is an increase in local code length.

In many code bases that lived long enough, that means screens and screens of functions inside the module/class files. It is still easier to navigate than between many files, but not by that much in practice (back/forth keyboard shortcuts go a long way to alleviate this type of pain)