In Windows Server 2016, the Telnet Server is no longer included. This was done in an effort to eliminate the security risk that Telnet presents. Telnet has been around since 1989 and was first used as a way of connecting to mainframes from remote terminals. Early on, it was used in private networks where security was not the heightened concern that it is today.
Now, with everyone connecting to the internet, these types of security holes have to be addressed. Just because something is “what you know” or “what you are used to” doesn’t make it acceptable anymore. Telnet was a quick and easy way of connecting to a server and running text-based commands from the command prompt. The transmission back and forth has no encryption so anyone watching can monitor the text for passwords or useful data.
Security is a never ending battle but this is just one more step Microsoft is taking to help in the fight.