There are basically political reasons for this. Wade-Giles is associated with Taiwan, and is in fact mostly used when referring to Taiwanese subjects, I've always seen Kaohsiung for the city, never Gāoxióng.
The Mainlanders would find it very insulting to not use Pinyin when referring to subjects in the PRC, so understandably, American journalism goes along with that.
For what it's worth I think both systems have different disadvantages, in that neither does a good job of reflecting the actual pronunciation of Guoyu. Excuse me, Putonghua. Doing so with the English character set isn't actually possible.
It's not the character set that's the problem so much so as the set of phonemes. English just doesn't have the ʂ/ɕ distinction, and no amount of creative spelling choices can fix that. Other things are much more straightforward, tones aside.
The Mainlanders would find it very insulting to not use Pinyin when referring to subjects in the PRC, so understandably, American journalism goes along with that.
For what it's worth I think both systems have different disadvantages, in that neither does a good job of reflecting the actual pronunciation of Guoyu. Excuse me, Putonghua. Doing so with the English character set isn't actually possible.