To the extent that what you are saying is true, it is only true because these companies have walled themselves off. You used to be able to chat with Facebook users over XMPP even.
It just sucks for the internet. I don't think, if those companies ceased to exist, that they would automatically get recreated because of some inevitable niche or market law. I think that they got where they are because of a fluke of the times they were created in -- people could not grasp how they make money.
In large scale, what you're asking is more dubious. If you concede that the United States alone has 11 major cultures, then you have to begin a process of "on-boarding" everyone onto your new, structured culture that your platform is designed around. That's why these debates about who is represented in the building of the platform come about, because under that model those concerns take center stage and they should.
I guess what I'm saying is the whole problem never needed to exist. There's better ways to share information than being on one platform.
If our dictionaries vary to much in their definitions then our communication becomes more and more difficult.
Maybe dictionary is not the best analogy (this is just an analogy) but I hope I'm getting my point across with this example.