Every competent FTP client I can think of can also handle SFTP and FTPS connections. With SFTP it's just a matter of telling the client that's what you're using so it can change to the different port; with FTPS you don't even have to do that.
It's true that people resist change, but the change they have to swallow here is so tiny and the upside so massive that it's darn close to malpractice to continue giving them the option to use plaintext FTP.
I once had trouble with a client who used his business data solution for uploading data to our server (we support FTP, FTPS and SFTP, and we recommend SFTP + keys). It was an old java-based application with no updates, no SFTP support, and all attempts at FTPS failed in the face of certificate issues (outdated list of CAs, no ability to force a certificate). The client had no understanding of the issue and the technician was an expert for this specific business application, with no ability (or willingness, maybe) to write any sort of script or workaround outside that application.
I think a lot of the problems we have with new protocols is that we simply can't add new ports. So many routers simply block anything that's not 80, 443, or 21.
It's true that people resist change, but the change they have to swallow here is so tiny and the upside so massive that it's darn close to malpractice to continue giving them the option to use plaintext FTP.