I noticed this excerpt:

"It is most commonly treated as a variety of Chamaecyparis obtusa in European and American texts,[1] but more often accepted as a distinct species by Taiwanese botanists.[3][4] The two taxa differ in ecological requirements, with C. obtusa growing primarily on drier ridgetop sites, while C. taiwanensis occurs on moist soils and with higher rainfall and air humidity."

I wonder if the amount of oil might be in part due to growing in high humidity. I assume the oil acts to repel bugs, and Taiwan certainly has those!