Telnet has been obsolete since the turn of the century. That doesn’t mean that nobody uses it but it does mean that everyone who does should be upgrading away from it.
Trusting the network for security was common in the previous century but standards have improved since then. For example, sending your password in clear text is no longer considered acceptable by mainstream security standards since it avoids the risk of passive network monitoring or accidental exposure.
Obsolete means no longer in use or useful. It's been argued in this thread that it's both in use and useful. But yes, there are more secure protocols that overlap with most of what telnet can be used for.
Obsolete doesn’t mean something has no possibility of being useful but rather that it’s no longer commonly used because there are better alternatives. My son’s beloved steam locomotives still run but nobody uses them for normal commercial service because they became obsolete shortly after the invention of diesel and electric.
> (of words, equipment, etc.) No longer in use; gone into disuse; disused or neglected (often in favour of something newer)
Bringing that full circle, telnet used to be common but it has security issues (lack of encryption or integrity unless you tunnel over TLS, lack of modern authentication options, etc.) and so anywhere it’s still used we should be looking in to replacing it.
As discussed in the thread above, there are scenarios in which lack of encryption etc is simply not relevant. And when that is the case, why would you prefer a more complicated protocol with more moving things that can go wrong?
Telnet is still in use for its primary purpose, which is a bit different than a locomotive which has been neglected to a tourist attraction. Your last paragraph means you would like to make telnet obsolete, but it isn't yet. As evidenced in the thread, it's not partical or desirable to replace it with other technology in all the deployments of it. So, it's still hanging in there for now.
Trusting the network for security was common in the previous century but standards have improved since then. For example, sending your password in clear text is no longer considered acceptable by mainstream security standards since it avoids the risk of passive network monitoring or accidental exposure.