Why isn't there a universal + standard VoIP/data SMS-like message protocol?Corporate Capture. If there were a universal protocol used by the big platforms then people could use one application to connect to each.
Has there been standards before?
This used to be a thing with MSN, ICQ, AIM, Yahoo, etc... They each had their own standard but the difference from today is those standards were open and one could connect directly to them with a stand-alone application. Pidgin, Trillian, others. It used to be people could use one application to connect everywhere thus avoiding most telemetry, advertisement, etc... That is precisely what they do not want. They want to control the flow of data and capture advertisement monetary options for all users. There are web tools today to strip telemetry and advertisement but they know most people on mobile devices will not bother to do this whereas a stand-alone application that could connect to everyone would just ignore the telemetry requests and advertisements on everything. It's also easier to force people to receive advertisements if they control the full data flow meaning if someone blocks it they can break the application flow "It appears you are using an ad-blocker" and such. With a single stand-alone tool people could choose to move to any platform easily.
What's more, with a single stand-alone application it is easier for people to properly E2EE/MLS encrypt conversations such as OTR (off the record) or other custom tools and exchange keys out-of-band making lawful intercept on the server impossible on all platforms. If people start encrypting their conversations not only is lawful intercept impossible but they can not use AI to learn what people are talking about. One simply connects to any small semi-trusted XMPP/IRC to exchange keys/identities then one need only share a fingerprint on the big platforms to boot-strap secure communications. OTR was just an example. It is in desperate need of forking and enhancements. Some big platforms claim to use E2EE but it is literally impossible for a server to manage this without having a way to inject something to perform lawful intercept. E2EE must be managed entirely out-of-band by a stand-alone open source client not controlled, created or contributed to by any of the platforms. When people argue against this they are just invoking a coping mechanism.
In summary, big platforms will never implement open protocols and open them directly to the public until such a time they can address all the capabilities mentioned. Corporate capture, advertising, AI monitoring, lawful intercept preventing user MLS encryption.