Why is there no Teams CLI?

There's a libpurple plugin, so you can in theory use Teams chat from Pidgin, finch, or other clients. I tried it last year and it didn't work very well.

There is an API:

https://learn.microsoft.com/en-us/graph/use-the-api

I've been using it recently and aside from some weirdness around permissions, it's decent.

If you need a CLI wrapper I'm sure an agent could make it for you in an hour or so.