I've had quite a recent situation where telnet did the job and ssh didn't:
Connecting to a newly-imaged board as part of the programming process.
You can do it for one board with ssh using a pre-generated key in the image, but then each subseqent board generates a 'Help the other end of the connection has changed - refusing to connect'. So far as I could tell there is no way to tell ssh not to do that, so it was entirely useless.
Telnet just worked, and in this case was being used on an internal wired network, firewalled by the programming machine so the use of cleartext logins really didn't matter.
And telnet is still a really useful testing tool for checking out if a port/service does what you expect. Sometimes nc will do instead but telnet is generally more convenient.