For the same reason that if you want to insult an English teacher, you say 'English is a Mickey Mouse subject'. 

And while Pandaren predate Kung Fu panda, they were concieved of as a joke.  I haven't taken the Panda-related crap in this expansion very seriously. 

Calling something Mickey Mouse is not the same as calling something Disney.  Disney is a multifaceted company with some very dark films (A space film where the captain turns his crew into zombies and flies into a black hole ending up in Hell.  An animated film where the main villain is based on Satan and shows some graphic violence) They also have hugely successfully and awesome films like all the recent Marvel movies and now Star Wars. 

Its an insult that doesn't fit, just like your usage of Mickey Mouse.  Since you know he is a widely loved figure that has made billions over the years.  Does it really matter how the original idea for Pandaren were thought up as?  What matters is what they are now and it is far from a April fools joke.  However even with all the joke references to them the RPG (which isn't Cannon) and the artwork has always had a non joke manner to them. 

Why wasn't Cataclysm a joke expansion for adding goblins and all their joke and stupid references? 

"Man is his own star.  His acts are his angels, good or ill, While his fatal shadows walk silently beside him. "-Rhyme of the Primeval Paradine AFC 54
You know a community is bad when moderators lock a thread because "...this isnt the place to talk about it either seeing as it will get trolled..."

mickey mouse is an insult used here in the uk, mate.  its probably been lost in the culture.  if someone supports what you would personally conceive to be a lesser football club than yourself, its termed as a mickey mouse club.  its just the way it is, like it or lump it.  its the same with what would be considered lesser cup competitions.  the europa league & what used to be the intertoto cup as mickey mouse competitions. 

Wait, RPing fat, food loving Pandas straight out of Kung Fu Panda is OK, but you draw the line at saying nom nom? 

Where does the fact that one of the races landed on a rocket ship straight out the Jetsons lie? 

1.  There's more to the Pandaren than 'lol kung fu pandaz!!11!!!' 
2.  Those traits come from real life pandas.  Kung Fu panda did not make it up, and Samwise's ideas predate kung fu panda anyway.  And neither of them are the first people to have pandas doing kung fu.  It's just a combination of an anthropomorphic chinese animal doing chinese martial arts. 

"If you have to believe it on faith, you have no reason to believe it at all.”  Aron Ra

This, is by far one of the most annoying things currently in wow for me.  To anyone whos not an rper they probably don't care much, but as an rper, seeing this joke played on by blizzard with there racial language barrier, if any perpetuation of what is childish about pandaren was ever present, its this it. 

It feels like when any other race is talking in there racial language, that the the devs put some thought into it, tauren, troll, draenei, forsaken, seemed like they made the effort.  This however, when trying to rp with someone, its worse then having someone coming to troll your event, because its consider a legitimate language? 

I think it is amusing.  Especially as a Mage I can speak in it and confuse people.  Really hardly anybody uses languages anyway, and if they used crap like "Xin cao win ching" they would be called racists.