Why are Oxyuranus snake species named Taipan?
An answer is found at the Wikipedia page for Taipan:


  The common name, taipan, was coined by anthropologist Donald Thomson after the word used by the Wik-Mungkan Aboriginal people of central Cape York Peninsula, Queensland, Australia.


This passage is citing Sutton. 1995. Wik Ngathan Dictionary as support. I cannot evaluate the truth in this statement though.

For another reference see McKnight. 1981. The Wik-mungkan concept Nganwi: a study of mystical power and sickness in an Australian tribe. Bijdragen tot de Taal-, Land- en Volkenkunde 137, which refers to Taipan as the Rainbow serpent (an Aboriginal mythical creature) of the Wik-Mungkan tribe.

Even more folklore is found in McNamee. 2000. The Serpent's Tale: Snakes in Folklore and Literature in "Taipan the snake and the blue-tongued lizard".