Because it's there.
Also most linux containers do not ships with such binaries to save on img size and reduce vuln management overhead.
$ ls --human --size --dereference $(which telnet)
144K /usr/bin/telnetThe point of reducing the amount of binaries shipped with the image is also to reduce the amount of CVEs/vulns in your reports that wouldn't be relevant for your app but woulld still be raised by their presence.
Debian also isn’t shipping telnet in the base install since Debian 11.
I mean technically MS Windows 10 is ten years old, but the big upgrade wave to 10 only happened like 4 years ago, which is quite recently. Maybe that is similar to macOS users, I don't know that.