To understand why an anime should be dubbed in a specific language, we have to know the factors to be considered . These factors are also the ones that the TV networks are thinking about in making their decisions. There are lots of factors, but basically there are two important ones...

The Anime Itself: We really have to consider the anime itself. There are lots of things that must be considered from an anime. The plot, the character... sometimes the general feel or tone of the anime. Sometimes, the genre of the anime to be dubbed is the one that determines what language should be used. For example, try dubbing a sci-fi anime in filipino. Technical terms such as "laser cannons", "pin-point barrier sheild", etc. will give the translator a headache. To directly translate those terms in filipino would sound very awkward...anyway, ano nga ba tagalog ng laser? Sometimes the translator can afford to keep those technical terms in english and the rest in filipino(for example,Neon Genesis Evangelion: terms like "AT field", "dummy plug", etc.), but what if the anime is full of those terms? Don't tell me the translator would leave everything in english? We didn't call him "translator" for nothing.