Multiple files would mostly just make them more fiddly to work with, juggling all these buffers. In my experience, the modern fashion for tiny source files is not intrinsically better, especially when all the code is related to a functional area (and is mutually recursive, in a compiler's parser).

You'd still rely on search to navigate, and whether it's in the same file or a different file is just an IDE / editor detail. If anything, fewer source code files meant you always knew which file to switch to to find any given function, which you could in turn find with an incremental search.