I believe that random Windows authoring software is vaguely more likely to have FTP built in than SFTP. (But finding good SFTP software for Windows, e.g. WinSCP, is not hard, so this is not much of an argument.)
It's also the case that SFTP requires giving someone an actual user account on your UNIX box, and preferably knowing enough about how to set SSH up to restrict them to SFTP access only. If your server is much more valuable than the data and you don't trust yourself not to get SSH configuration subtly wrong, it's not terribly unreasonable to prefer installing an FTP server to adding a local user and giving someone else a password to it.