You noticed it too in episode 16? that is indeed weird... But something else that is strange, how can minotaurs exist in there? minotaurs are formed of a human body and a bull's head. Maybe there are humans in Equestria, but they haven't been introduced yet?
That sounds very likely, but if that's the case I believe it's the other non animal creatures that don't want to be seen in Equestria, probably in a similar way that Dragons think very poorly of pony kind and their lands which leads to them almost never visiting Equestria.
That or maybe, as addressed in one story, they are rather racist towards Humans. Humans=animals right? They are still animals so I'm guessing they are racist in a way. (They are just so sheltered that they are? If you get that. )