Who does that?
I am linguist. And when it comes to a unified language system in a given country, it behooves you to have one language (officially).
Otherwise, you open yourself up to the risk of diglossia, which in our case would result in distinct "regional dialects" which may be indistinguishable from one another. Engrish, Spanglish etc. Moreover, it relegates "proper English" to the realm of the universities, creating a class stigma for those who do not speak it.
For example, my language field is Semetic languages, specifically Arabic and its dialects. Due to a number of factors: colonialism, nationalism, a lack of interstate commerce, and a laissez faire policy on a unified language... "Arabic" does not exist. There are 28 official dialects, many completely indistinguishable from one another. And on top of that, there is a written language (which once upon a time was Arabic, or close to it), that only university graduates speak.
The goal of language is to create shared meaning. No one language is better than another, but if you intend to get your meaning across, you'll have greater success communicating in such a way that you're understood by the most people... That's French in France, Spanish in Argentina, and English in the U.S.