Aren't most protocols proprietary? Every app builds their own on top of standard protocols like HTTP, TLS, and IP. Not all services are hostile to third party clients though

well, there's proprietary in the sense of "not a standard" and proprietary in the sense of "no one else can make software that uses this protocol". the latter is very weird if you think about it.

Eh not really that weird. Consider how Microsoft repeatedly reverse engineered AOL for compatibility reasons and AOL actively blocked their efforts with every update: https://youtu.be/w-7PjunSxLU

Stuff like this happens all the time and the internet has always been like this. I'm sure older users will remember even older examples