Because the British empire was absolutely huge. Which lead to many countries having English as an official language. Which means those countries would conduct trade in English. Followed by American dominance, which also has English as its main language.

And that American dominance includes dominance in media, especially films because of hollywood. Technical documents, research and especially computer-related technical documents are mainly in English for the same reason.

Sure, English is not that hard of a language. But it’s not the easiest either.