@khm This is the problem having an open standard for online chat is meant to solve. We have at least 2; XMPP and Matrix, and most chat services don't interoperate over either.
Why? IMHO it's because you can justify much higher stock valuations if you can credibly promise to win the zero-sum battle to be the One Ring. And startup founders and early employees are paid for some or all of their early stage work in stock options.