The reasons why are tedious and complex but, as an illustrative example, one reason comes down to the way I use English (words, in the vulgar sense :-), and the way you use English and the way Jake, say, uses English are all ever so slightly different that sum to the necessity for having a ATinNM-to-Sven-to-Jake [& iterate]/English Dictionary & Grammar translation handy and start adding on every user, and every possible user.

She believed in nothing; only her skepticism kept her from being an atheist. -- Jean-Paul Sartre