I'm guessing British colonisation brought the English language in and I know many countries where they banned them from speaking their native language during the British empire.
This is actually what happened to us here in Nigeria, but it was prevalent in the urban centres, people in the rural areas weren't given stiff restrictions in terms of language prohibition except those who had court cases at the colonial bench.
These prohibitions in the urban centres have negative effects on the urban dwellers. Look at the effects on the populace in today's Nigeria.
Do they only speak English in the schools?
Yes! And this in collaboration with neocolonialism have made most of our cultural heritage to be buried underneath the ground. Young ladies are no longer proud of their mother tongue. The other day, listened to my neighbor telling her daughter to maintain the proper stress patterns in English while she spoke to her. It should be noted that I've never heard her daughter speak her native language.
Thanks for stopping by, I hope this explains the question.