Because there is no unambiguous word in the English language that means free "as in freedom." If you say free software, people will probably only think of price.

Oh, wait! This entire sentence is in a foreign language, except that word :)

Universal word and concept.

Because "free" can mean more than one thing: http://en.wikipedia.org/wiki/Gratis_versus_libre

Ce n'est pas 'fancy', ni 'foreign' à moi!