Email is mostly dead - we use Gmail (or Microsoft 365) now. It is to email what Slack is to IRC. With only one or two vendors, the need for widely interoperable protocols is gone - they only need to interoperate between a few large service providers, and that can be done by private agreement.
You realize those ESPs use and support the industry standard open protocols under the hood, right? Slack is 100% proprietary and does not use industry standard protocols for interchange or federation. These are not even remotely comparable. Slack would need to use industry standard and open protocols (i.e. XMPP) to allow federation with products like Teams and Discord for the situations to be comparable.
It does if your proprietary API is the industry standard. Everything Microsoft puts out is both industry standard and proprietary. So is everything TSMC puts out (their processes). Most of the interconnects in any computer system as well. I actually bought a legal copy of the SATA standard, for $30ish.
