Comment by WilTimSon

Because it helps preserve the country's unique culture and history, freeing it of the influence of a state that imposed its rule on them. I know some people prefer languages to be uniform but I don't see 'everyone speaks the same language' as a good thing. As a secondary option, yeah, it would be nice if everyone spoke English or whatever becomes the choice eventually. But I want culture to flourish and this is part of makes countries stand out.