I'm confused why you seem to think that because English is the most popular second language, that automatically means it is the best communication tool. Don't you think the reason it is so well-known is more because the US (and UK, to a lesser extent) is such a dominant force economically and militarily? That non-English-speaking states consider it important to learn, so they teach it early in school -- and then on top of that the largest film industry is in the US, so English content is pretty available?

I mean, there is a lot more external force going behind the dissemination of English than that of Toki Pona, so I dunno, seems pretty silly to attribute it's "success" (popularity) to some internal aspect of the language.