The thing is, GSN Monkey is the top demanded species of Chinese players while it is conceivable that most non-Chinese players are not interested. Since from the perspective of non-Chinese players, the East Asian primates are already represented by the Japanese Macaque, so no more is needed. GSN Monkey is completely absent in captivity outside of East Asia so the "realistic gangs" definitively refuse it. Why demanded by Chinese players, b/c the GSN Monkey is considered a "national treasure" and one of the icons of Chinese fauna, and fills the gap of Chinese primates (Lar Gibbon has been extirpated in China for about 20 years). The natural habitat of GSN Monkey overlaps a lot with the Giant Panda, so it is an essential addition to the themes related to Panda like Sichuan Basin or Qinling Mountain. Someone may argue why Chinese players' thoughts matter, b/c about 21% of PZ players are Chinese, which is more than players from any other country.
Since the support almost ended and the slots of animals are almost full, I am not expecting the Frontier to offer GSN Monkeys, I just wait for the good Mod of them, the Mod I found doesn't do a good job due to the weird head (the GSN Monkeys IRL have bump-liked head, but the Mod one has flat head) and lack of the long mantle on their back, it looks like the Modder made the GSN Monkey based on Proboscis Monkey's model, but they have significantly different head shape.