There goes your answer, @kbaker116: the "Giant Forest Hog" in SDZ is probably a melanistic river hog...
So why are there no Giant Forest Hogs in Western collections?
1. They're not the easiest pig species to keep, requiring ample heating, space and a high-quality diet. The ones kept in Frankfurt and Antwerpen in the past thus didn't last long...
2. Similar to other African pig species, exporting them from Africa is very difficult, due to the fear ofspreading epidemic diseases such as African and European Swine Fever to domestic pigs in Europe and America.
3. To be honest: Wild pig species aren't the most popular species in zoos. As the time of collecting rare species for zoos just for the sake of displaying them is pretty much over in the Western zoos, hardly any zoo is interested in obtaining a species only die-hard zoo and wildlife fans are interested in.
Besides, there are other, highly endangered species such as Chaco peccaries (not really a pig, but I still count them in), or Negros and maybe soon Javan warty pigs that should rather be kept.