Part of it to be fair comes to telnet being ubiquitous. I've used any number of aix / hp-ux / solaris / Linux / windows / whatever systems over the decades, with limited or high privileges, and telnet was the one command that worked on all and could within 3 seconds and no fancy docs or knowledge and additional tools tell me the basics of what I needed to know. Are there better tools? Ab so freaking lutely. But telnet is there :-)
Twenty years ago, sure. Yet I every time I have the urge to use telnet on a modern system, I have to install it. You may as well install netcat if it is available (and if it is suitable to the task).
I had to point out that one may as well install better tooling more appropriate to the domain if one would have to install telnet, some years back. (-:
My 100 Croatian lipa