Perhaps because Unown sucks and only the great and superfabulous Pokemaster can bring out its true potantial (/030)/
Really though, if you look at the date PM's answer was in 2010. The other three are from 2014. Compund that with the aforementioned fact the Unown sucks, Pokemaster already said all there is to say. Considering that his answer amassed an average of 1 upvote every 2 years before the next answer, I wouldn't call it a special case or anything.