If what you write were true, it would have happened a very long time ago.
But it didn't. Why?
Because a language is basically like a uniform that marks "us" vs. "them". It creates group cohesion and community.
To be exact any non-English language, because English is spoken by anybody anyway, therefore does not give any identity.
English-speakers everywhere (be it a native US or a cosmopolitan European or Chinese) are having very few children and are living in a destructive "pop culture" that is not very conducive for large families.
Non-English-speakers on the other hand are isolated from "pop culture" a lot better, therefore can have more stable and larger families - and are growing in all countries.
That trend can be seen everywhere. Traditional English speakers will be a minority in all the major English-speaking nations (US, UK, Australia). Maybe they can hold out and maintain a majority in New Zealand.
A good example are the Amish: Just 200 Swiss/Germans came to America and they did NOT assimilate. 200 years later they are 250,000 and still doubling every generation. That is only possible because they are isolated from the majority culture - and their ancient German dialect is one of the things that helps them do that: If the children don't understand Lady Gaga, they won't be influenced by her.
And that is the reason why no language replaced all the others: When the dominant culture/language becomes decadent, people have no other choice than to push other cultures/languages in order to survive.