As a non-native speaker using English daily with other non-native speakers, I must say that it is the ideal global lingua franca. First of all, it is very open-minded about "broken" pronounciation and minor grammatical errors ("Bad English" is actually a thing). In contrast to other big languages, it is not as obviously tied to a single nation or culture - so everyone can make it "theirs". (Other large languages expect perfection and a non-native speaker will be treated as intellectually inferior)
I think one explanation for this could be that English itself stared off as a hybrid language (Germanic Saxon/Scandinavian mixed with Latin midevial French - and possibly some ancient Celtic in the mix).