I don't know if people still think about this but here's the explanation.
The reason why orcs look like pig monsters in japanese stories is due to a mistranslation in their D&D manual of monsters. Orcs are usually described with having pig like fangs and some small pig like details. However in ther manual they translated as if orcs were pig-like creatures instead. It's the same reason as to why their kobolds look like dogs instead of lizards where D&D kobolds were tiny lizardmen with some dog-like features in their faces, but they were translated as being dog-like instead.
Anyway this error persisted for too long until if became the norm for them. Much like how people nowadays can immediately relate to virus-mutated-epidemic-spreading-creatures as being zombies, instead of spirit-possessed-corpses, which is what zombies should really be.