I was playing TP today and thought of this very thing and ways to explain it. Link cannot talk to the boars or to the Ordon goats and they seem to be pretty "neutral" animals. (I *love* riding the boars, by the way. They have a different feel to them than Epona and I just think they're neat).
Maybe Nintendo thought "these types of animals/livestock are too stupid for an intelligent wolf to talk to" - This...would make no sense as anyone who has cared for goats knows, they're smart-alecs. Pigs, though an unfortunate combination of smelly and tasty, are one of the smartest mammals around. (I have an online friend who tries to avoid eating pork on the grounds that he's uncomforable eating something with a high intelligence level). I just had some bacon, myself...
Maybe goats, pigs and other untalkative animals just don't know Wolf Link's language. Perhaps there are certain dialects to the psychic-animal speech that goes on and they just don't share a language with Link.
Maybe they don't speak to him because the wolf is a major predator to their kind and so it's a culture/class barrier. Epona only talks to him because she smells or senses her master behind those sharp fangs.
Maybe boars and goats are smart and they know it and are too stuck up to talk to a "dumb" wolf?
There are my possibilities, including "Nintendo felt it uncessary or was lazy." This is weird because you can have useless chit-chat with *frogs* in this game if you know where to find them.