partly because I work for a large company that is deeply integrated with MSFT teams. Also, at that size, we don't usually have such team level autonomy. Lastly, they don't want us routing any information through a 3rd party. Confidentiality and security is critical.

In general, mature teams do not adopt entirely new communication styles just because they are better. It usually takes something that is either revolutionary (eg: when Slack first got popular as a move away from email). Or, it is a seamless addition to what they already have and doesn't rock the ship.