The two teams in the World Series are the best in the world. Many other countries see the MLB as the premiere baseball league and therefore the best players in the world play in the league. The team that wins the World Series is seen as the best in the world so therefore it is justifiable to call the MLB championship the World Series.
I really would not complain about it, if it where theoretically possible for other countries to participate. But it isn't - the World Series has nothing to do with the World just with an approach that is as well self-focused and overly self-confident.
It's confusing, wrong and absurd to call it the World Series or the Miss Universe Contest. And while the last one at least (most likely) doesn't offend someone, the term World Series does quite a bit. North America is not America. And it's not the World. Just that.
Its plain an simple ridiculous to call something the world series when one nation is involved in it. Its just like when the play Junga-Junga (not a real game) in Pakistan that they do not call it the Universe Junga-Juang championships. But seriously America sucks so lets get angry at me.