In fact, editors used to be one such concern, when they were limited or getting extremely slow with large files. Also old-style version control like CVS was so

In fact, editors used to be one such concern, when they were limited or getting extremely slow with large files. Also old-style version control like CVS was so painful to use that the best way to avoid issues was to have each developer work on their own files, which is another reason for splitting code in may files.