Why Do Characters in the Anime Refer to All Pokemon as "It?"

I don't know. It is annoying though. Sometimes they'll refer to the gender like in "Memories are Made of Bliss" Dawn hugged Piplup when he was about to cry and told him, "You're a big boy." Also, in "Diancie and the Cocoon of Destruction" when Argus was watching Diancie on video he said "If Diancie escapes we'll never be able to find her again." or something along those lines, but Argus did refer to Diancie as a girl.

Probably because they don't know whenever it's a male or a female. Although i do find it odd that they continue calling a pokemon an "it" when its obvious it's a male/female