Apples and oranges comparison, one is a messaging app, the other two are used for communication and collaboration across teams in a workspace. I have worked in 5+ companies who used either Slack and Teams, none used Telegram for any comms.

Telegram is 'bot friendly' since the beginning, gaining a lot of users with crypto boom a decade ago with coin drops and things like that, so it is very good to develop for, but I have your initial sentiment first - shame this hasn't launched with tools people actually use for work.

And no, Discord is not used for that either.