SuKi us very right. The lingua franca is mostly the language used in the most powerful country or countries in a certain era. Remember that is was not always English. For a long time it was Latin (until ~1700), later French (~1700-1900), now English, maybe in a few years it is Chinese? 

1.Most of people speak English...

2.It`s very melodical and laconic language - good for musicians))). For ex. for me it s really hard to sing in Russian (my mother tongue) and I better sing and compose in English. Remember singers of 80s... most of them prefered to sing in English.)))