It's widespread popularity. Everyone wants to learn it and with just that one language, you can go so many places. Also the literature in English is great like Shakespeare, Dickens etc. though I haven't read too much of the classics hehe. Most importantly English is universal. Most people you meet will know a little bit of English or want to try learn English so English connects you with people and you meet heaps of friends. Without knowing how to speak English, I wouldn't survive where I am :)