Plus there are certain things that happen at startup, and if you typed code into the repl that broke one of these, you wouldn't know.
Ah, I take it you're not a fan of the old Lisp/Smalltalk approach of image-oriented development, where tweaking the running system is the canonical version of the code?
(Apologies if one of your essays already covers your views on that; I don't remember it being mentioned, and a quick search didn't turn up anything.)
It's not hard to imagine someone reinventing it as an advanced version of the Smalltalk approach: add the ability to view multiple definitions in some predefined order, add control over indentation (no small thing), add the ability to intersperse comments between the definitions, and bingo, you've reinvented the text file.
A lot of the lisp-machine veterans are, but I agree most current lispers aren't. One reason, though, might be that no recent Lisp actually provides a good environment for image-oriented development (the facilities for inspecting/manipulating the running image are a lot clunkier than those in, say, Squeak).